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Gear Talk => EOS Bodies - For Stills => Topic started by: Knut Skywalker on July 15, 2013, 01:59:12 AM

Title: How (and why) does sensor size change DOF?
Post by: Knut Skywalker on July 15, 2013, 01:59:12 AM
Hey guys,
I've read it multiple times now and i really dont understand it. Why does the sensor size affect the DOF and why do FF cameras have a smaller DOF? Seems like a pretty basic question but i really couldn't wrap my head around this concept.

Greetings from Germany,
Knut Skywalker
Title: Re: How (and why) does sensor size change DOF?
Post by: ecka on July 15, 2013, 02:33:45 AM
DoF ~ focal length * aperture * subject distance
If you want to shoot the same picture using the same lens with both FF and crop sensor cameras, you need to be closer to the subject with FF camera to get the same framing and that's the only difference.
Title: Re: How (and why) does sensor size change DOF?
Post by: privatebydesign on July 15, 2013, 02:39:11 AM
DoF ~ focal length * aperture * subject distance
If you want to shoot the same picture using the same lens with both FF and crop sensor cameras, you need to be closer to the subject with FF camera to get the same framing and that's the only difference.


That is only part of the story, and there are many ways to tell it........

For a very good explanation look here. http://en.wikipedia.org/wiki/Depth_of_field (http://en.wikipedia.org/wiki/Depth_of_field)

Specifically:-
Quote
Relationship of DOF to format size

The comparative DOFs of two different format sizes depend on the conditions of the comparison. The DOF for the smaller format can be either more than or less than that for the larger format. In the discussion that follows, it is assumed that the final images from both formats are the same size, are viewed from the same distance, and are judged with the same circle of confusion criterion. (Derivations of the effects of format size are given under Derivation of the DOF formulas.)

“Same picture” for both formats
When the “same picture” is taken in two different format sizes from the same distance at the same f-number with lenses that give the same angle of view, and the final images (e.g., in prints, or on a projection screen or electronic display) are the same size, DOF is, to a first approximation, inversely proportional to format size (Stroebel 1976, 139). Though commonly used when comparing formats, the approximation is valid only when the subject distance is large in comparison with the focal length of the larger format and small in comparison with the hyperfocal distance of the smaller format.

Moreover, the larger the format size, the longer a lens will need to be to capture the same framing as a smaller format. In motion pictures, for example, a frame with a 12 degree horizontal field of view will require a 50 mm lens on 16 mm film, a 100 mm lens on 35 mm film, and a 250 mm lens on 65 mm film. Conversely, using the same focal length lens with each of these formats will yield a progressively wider image as the film format gets larger: a 50 mm lens has a horizontal field of view of 12 degrees on 16 mm film, 23.6 degrees on 35 mm film, and 55.6 degrees on 65 mm film. Therefore, because the larger formats require longer lenses than the smaller ones, they will accordingly have a smaller depth of field. Compensations in exposure, framing, or subject distance need to be made in order to make one format look like it was filmed in another format.

Same focal length for both formats
Many small-format digital SLR camera systems allow using many of the same lenses on both full-frame and “cropped format” cameras. If, for the same focal length setting, the subject distance is adjusted to provide the same field of view at the subject, at the same f-number and final-image size, the smaller format has greater DOF, as with the “same picture” comparison above. If pictures are taken from the same distance using the same f-number, same focal length, and the final images are the same size, the smaller format has less DOF. If pictures taken from the same subject distance using the same focal length, are given the same enlargement, both final images will have the same DOF. The pictures from the two formats will differ because of the different angles of view. If the larger format is cropped to the captured area of the smaller format, the final images will have the same angle of view, have been given the same enlargement, and have the same DOF.

Same DOF for both formats
In many cases, the DOF is fixed by the requirements of the desired image. For a given DOF and field of view, the required f-number is proportional to the format size. For example, if a 35 mm camera required f/11, a 4×5 camera would require f/45 to give the same DOF. For the same ISO speed, the exposure time on the 4×5 would be sixteen times as long; if the 35 camera required 1/250 second, the 4×5 camera would require 1/15 second. The longer exposure time with the larger camera might result in motion blur, especially with windy conditions, a moving subject, or an unsteady camera.

Adjusting the f-number to the camera format is equivalent to maintaining the same absolute aperture diameter; when set to the same absolute aperture diameters, both formats have the same DOF.

Also here, http://www.josephjamesphotography.com/equivalence/ (http://www.josephjamesphotography.com/equivalence/) for a very detailed insight into sensor sizes and their interaction with focal length, dof, aperture and iso. Yes, even iso has a crop factor!
Title: Re: How (and why) does sensor size change DOF?
Post by: ecka on July 15, 2013, 03:17:20 AM
DoF ~ focal length * aperture * subject distance
If you want to shoot the same picture using the same lens with both FF and crop sensor cameras, you need to be closer to the subject with FF camera to get the same framing and that's the only difference.


That is only part of the story, and there are many ways to tell it........


Well, for me it is a very simple thing and I gave a simple answer to the question "Why?". You don't need to write a book to answer a simple question, because that's how people get confused.
Title: Re: How (and why) does sensor size change DOF?
Post by: tortilla on July 15, 2013, 04:08:27 AM
Why does the sensor size affect the DOF and why do FF cameras have a smaller DOF?

It doesn't. But you use larger focal lengths on FF cameras, and the larger the focal length, the smaller is the DOF.
Title: Re: How (and why) does sensor size change DOF?
Post by: mik14 on July 15, 2013, 05:12:07 AM
That is only part of the story, and there are many ways to tell it........
There's no "story". DOF is a characteristic of a lens and has nothing to do with sensor size. End of story.
Title: Re: How (and why) does sensor size change DOF?
Post by: neuroanatomist on July 15, 2013, 05:19:17 AM
There's no "story". DOF is a characteristic of a lens and has nothing to do with sensor size. End of story.

You couldn't be more wrong. Perhaps you're stuck in the circle of confusion...   ::)
Title: Re: How (and why) does sensor size change DOF?
Post by: rs on July 15, 2013, 05:50:57 AM
Another way of looking at it is to exaggerate and think of a very small sensor camera (iPhone) vs very large sensor camera (medium format). If both are equipped with a lens to give the same angle of view, then other than scale, they do pretty much the same thing.

Image a scene with a subject at about 2m and a background at about 10m away.

The phone sees that scene in front of it as being relatively massive - almost like how an insect would see it - so anything beyond about a metre is effectively infinity, meaning its pretty much all in focus. Put that same scene in front of the medium format camera, and everything is much smaller relatively speaking to the camera - so none of it gets close to infinity (more like a macro shot), so the depth of field is much narrower.

It's a little bit like taking a photo of a really scaled down version of that scene in macro mode with the iPhone.

Obviously the differences are much less when comparing FF and APS-C, but the differences are still there. 
Title: Re: How (and why) does sensor size change DOF?
Post by: badgerpiper on July 15, 2013, 05:51:33 AM
There's no "story". DOF is a characteristic of a lens and has nothing to do with sensor size. End of story.

You couldn't be more wrong. Perhaps you're stuck in the circle of confusion...   ::)

If you take two pictures at the same position with the same lens on both a crop and a full frame, the distance between the nearest in focus object and the furthest away in focus object will be the same, so the depth of field does not change. Obviously the image captured will be different on each.

However, if you're talking about the depth of field for an equivalent picture, you'd have to move the full frame camera closer which would result in a reduced depth of field.
Title: Re: How (and why) does sensor size change DOF?
Post by: Grumbaki on July 15, 2013, 06:08:43 AM
Let's try to help

DoF ~ focal length * aperture * subject distance

in this "equation",

Focal lenght =
- on FF, just the number you see on the lens/EXIF
- on ASP-C/H, number of the EXIF * 1,6/1,3

thus just changing the sensor changes the focal lenght and by repercussion the DoF.

I can't find a simpler way to put it.
Title: Re: How (and why) does sensor size change DOF?
Post by: ecka on July 15, 2013, 06:32:58 AM
Let's try to help

DoF ~ focal length * aperture * subject distance

in this "equation",

Focal lenght =
- on FF, just the number you see on the lens/EXIF
- on ASP-C/H, number of the EXIF * 1,6/1,3

thus just changing the sensor changes the focal lenght and by repercussion the DoF.

I can't find a simpler way to put it.

Wrong. The only thing that changes is the field of view. Focal length stays the same.
Title: Re: How (and why) does sensor size change DOF?
Post by: GaryJ on July 15, 2013, 06:42:22 AM
Love you guys...... ;D
Title: Re: How (and why) does sensor size change DOF?
Post by: jdramirez on July 15, 2013, 06:50:20 AM
I don't think it does.  Yes there are people who claim it is greatly affected, but I'm not sure they are right. 

The lens focuses the image onto the sensor.

With full frame, more of the area is captured, but depth of field is unchanged.

http://improvephotography.com//wp-content/uploads/2013/02/how-a-lens-works.jpg (http://improvephotography.com//wp-content/uploads/2013/02/how-a-lens-works.jpg)

So the corners are improved because they are excluded.  I've heard there is a half stop of depth of field that is changed... and that seems minor enough to be true... but that I'm not sure about.
Title: Re: How (and why) does sensor size change DOF?
Post by: tdrive on July 15, 2013, 07:01:57 AM
My understanding of it is that compact cameras have a larger Depth Of Field to a full frame because it is dictated by ACTUAL focal length, NOT EQUIVALENT. A 35 mm camera on a standard lens wide open is about 24mm. On a cropped camera it is about 18mm and on a compact somewhere about 6mm
http://dpanswers.com/content/tech_crop.php (http://dpanswers.com/content/tech_crop.php)
Title: Re: How (and why) does sensor size change DOF?
Post by: privatebydesign on July 15, 2013, 07:53:06 AM
Oh dear,

Anybody that wants to argue the point really needs to read my two links, and get a background understanding on the CoC, circle of confusion.

The first thing you have to do when trying to understand this dof stuff is set a standard for your comparison. If we are going to assume a same sized reproduction, ie 8"x10" print or "fill screen" on the same monitor, and frame the image the same while shooting from the same place, you have to take everything into consideration.

Here is a comparison I did a while ago for another thread much like this one. It is a comparison based on the above criteria. The three images are identical in dof, noise, perspective, angle of view, etc etc.

If you read and understand the quote from Wikipedia I posted you will understand if you change your comparison criteria you will change the dof characteristics.
Title: Re: How (and why) does sensor size change DOF?
Post by: Don Haines on July 15, 2013, 08:08:46 AM
This is a confusing topic because the term "1.6 x crop" is a bit confusing to some. You hear that when you mount a 100mm lens on an APS-C camera it behaves like a 160MM lens on a FF camera. Really, what it means is that the field of view is the same as if you had a 160m lens on a crop camera, but it does not mean you have a 160mm lens.

The lens remains a 100mm lens. It's optical qualities do not change, it's depth of field does not change, it's aperture does not change. When you mount that lens on an APS-C camera you are using a sensor that will only sample the center 40% of the image ( 1/(1.6^2)).

If you were to use a FF sensor with 46Mpixels that was built with the same technology as an 18Mpixel APS-C sensor, the center part of the FF image capture would be ABSOLUTELY identical to that of the APS-C image.

So, sensor size has no effect on DOF or aperture.
Title: Re: How (and why) does sensor size change DOF?
Post by: neuroanatomist on July 15, 2013, 08:42:29 AM
There's no "story". DOF is a characteristic of a lens and has nothing to do with sensor size. End of story.

You couldn't be more wrong. Perhaps you're stuck in the circle of confusion...   ::)

If you take two pictures at the same position with the same lens on both a crop and a full frame, the distance between the nearest in focus object and the furthest away in focus object will be the same, so the depth of field does not change. Obviously the image captured will be different on each.

However, if you're talking about the depth of field for an equivalent picture, you'd have to move the full frame camera closer which would result in a reduced depth of field.

In the former case, my head shot just became an eyes-and-mouth shot that I had to delete because most people like to see their whole face in a portrait. The latter case is far more relevant to most types of photography. The exception might be macro photography, where at 1:1 magnification, you are at the MFD of the lens, regardless of sensor size.  But at macro distances, DoF is incredibly thin anyway (and the assumptions made by most DoF calculators don't hold).

As for DoF being solely a property of the lens, what, subject distance no longer matters??

The real story is that DoF is determined by subject magnification and lens aperture.
Title: Re: How (and why) does sensor size change DOF?
Post by: rs on July 15, 2013, 08:47:28 AM
This is a confusing topic because the term "1.6 x crop" is a bit confusing to some. You hear that when you mount a 100mm lens on an APS-C camera it behaves like a 160MM lens on a FF camera. Really, what it means is that the field of view is the same as if you had a 160m lens on a crop camera, but it does not mean you have a 160mm lens.

The lens remains a 100mm lens. It's optical qualities do not change, it's depth of field does not change, it's aperture does not change. When you mount that lens on an APS-C camera you are using a sensor that will only sample the center 40% of the image ( 1/(1.6^2)).

If you were to use a FF sensor with 46Mpixels that was built with the same technology as an 18Mpixel APS-C sensor, the center part of the FF image capture would be ABSOLUTELY identical to that of the APS-C image.

So, sensor size has no effect on DOF or aperture.
That is all absolutely correct, except for one thing - in reality, if you moved from a crop system to a full frame system, you wouldn't take photos of the same scene from the same location with the same lens to end up with what is a wider framed photo.

As you say, if you do that and you crop it down, its identical to taking it with a crop camera.

But if you frame up the shot as you envisioned, either approximating it by altering your perspective by getting close, or ideally by keeping your perspective the same with a longer lens, presuming the aperture remains the same, the DoF is narrower with FF.
Title: Re: How (and why) does sensor size change DOF?
Post by: ecka on July 15, 2013, 09:09:43 AM
This is a confusing topic because the term "1.6 x crop" is a bit confusing to some. You hear that when you mount a 100mm lens on an APS-C camera it behaves like a 160MM lens on a FF camera. Really, what it means is that the field of view is the same as if you had a 160m lens on a crop FF camera, but it does not mean you have a 160mm lens.

The lens remains a 100mm lens. It's optical qualities do not change, it's depth of field does not change, it's aperture does not change. When you mount that lens on an APS-C camera you are using a sensor that will only sample the center 40% of the image ( 1/(1.6^2)).

If you were to use a FF sensor with 46Mpixels that was built with the same technology as an 18Mpixel APS-C sensor, the center part of the FF image capture would be ABSOLUTELY identical to that of the APS-C image.

So, sensor size has no effect on DOF or aperture.

Good explanation, with wrong conclusion. Using similar logic we can say that lens-sensor combo has no effect on DoF as well, only subject (scene) size and distance matters. DoF is not a constant describing the lens or the sensor, but it is described by the combination + distance.
Title: Re: How (and why) does sensor size change DOF?
Post by: TommyLee on July 15, 2013, 09:26:13 AM
DoF ~ focal length * aperture * subject distance
If you want to shoot the same picture using the same lens with both FF and crop sensor cameras, you need to be closer to the subject with FF camera to get the same framing and that's the only difference.


this is really it... good simple explanation...
 and badgepiper added  a bit more....

so
to get the same framing ...in the result.....you move closer on FF...
and closer....shrinks the DOF...
in basic terms...

this is all you need to keep in mind .....IMO....

Title: Re: How (and why) does sensor size change DOF?
Post by: Marsu42 on July 15, 2013, 09:43:27 AM
Here is a comparison I did a while ago for another thread much like this one. It is a comparison based on the above criteria. The three images are identical in dof, noise, perspective, angle of view, etc etc.

Admit it, since you knew they'd be the same you were lazy and they're all from the same camera :-p ... ok, just kidding.

Why does the sensor size affect the DOF and why do FF cameras have a smaller DOF?

In addition to the good explanations from privatebydesign above, here's what I personally tell myself: To get the same shot (i.e. field of view) on a ff camera in comparison to a crop, you have to walk towards the object with a ff, resulting in a thinner dof @same aperture.

This also means that in real life, camera-object range is equaly important for the resulting dof than your sensor size, you can get very thin dof shots out of a longer lens even @medium aperture like the 70-300L@f4 which is able to focus very near objects. Play around here: http://www.dofmaster.com/dofjs.html (http://www.dofmaster.com/dofjs.html)

Last not least, note that if people rave about thin dof they often mean "strong background blur" except if you like the "only the nose in focus" type shots, and same thing here: bokeh also strongly depends on focal length and object/background distance relationship.

PS: The phrase "ff has thinner dof" indeed confusing at first, /me also German :-p and I also had to refer to this site to get a proper explanation :-)
Title: Re: How (and why) does sensor size change DOF?
Post by: privatebydesign on July 15, 2013, 09:49:14 AM
Or you can mostly keep discussing it whilst completely ignoring the linked articles that explain it far better then any of us.  :)

What is dof? It is the distance at which a point is no longer a point but a circle (where something sharp is no longer sharp). The size of the circle or point is determined by the physical aperture (not the f stop value) and the subject magnification (not distance). Alone.

Depending on how you draw your comparison the sensor size can make a difference, or not.

Typical photo situations.

If you change either the physical aperture, not necessarily the f stop value (50mm f2 is the same as 100mm f4, they both equal 25mm), or the subject magnification, you change the dof characteristics.

Subject magnification is not limited to the size it is reproduced on the sensor, it continues through to final output size. Take a slightly blurry image and down size it to a thumbnail, it will look sharp, if you make something smaller the dof increases, conversely enlarging something more makes those points and circles easier to differentiate. Take a razor sharp image and enlarge it 400%, it will look blurry from the same place, step back and it will regain its apparent sharpness. Look at a billboard from across the street, it looks sharp, now walk up to it and the "pixels" can each be two inches large.

You have to determine your specific image and comparison criteria to determine dof.
Title: Re: How (and why) does sensor size change DOF?
Post by: neuroanatomist on July 15, 2013, 09:52:44 AM
Last not least, note that if people rave about thin dof they often mean "strong background blur" except if you like the "only the nose in focus" type shots, and same thing here: bokeh also strongly depends on focal length and object/background distance relationship.

Except that bokeh really refers to the quality of the OOF blur, independent of quantity.  But maybe that's a story for another day.  ;)
Title: Re: How (and why) does sensor size change DOF?
Post by: privatebydesign on July 15, 2013, 10:04:10 AM
Here is a comparison I did a while ago for another thread much like this one. It is a comparison based on the above criteria. The three images are identical in dof, noise, perspective, angle of view, etc etc.

Admit it, since you knew they'd be the same you were lazy and they're all from the same camera :-p ... ok, just kidding.


 :) No I promise they were from three different cameras. Having said that you could mimic the test with one camera and a zoom lens, just crop the zoomed in images.

I actually did the original for a talk I did on sensors, dof and other related camera stuff. Somebody said they were the same image until I pointed out some of the greenery moves between them!
Title: Re: How (and why) does sensor size change DOF?
Post by: randerson5726 on July 15, 2013, 10:42:13 AM
This has been confusing for me for a long time thank you everyone for clarifying it.

Here's my new understanding.
• Physically the DOF does not change because your not changing the lens (ie. set up a shot,  switch a crop to a FF, and you'll just get a wider field of view but same DOF).
• But in practice it essentially does change (ie set up a shot, switch bodies, now move the came to have the same field of view, now the DOF of the crop camera photo will be larger. Same goes for not moving the camera and changing focal length).
Title: Re: How (and why) does sensor size change DOF?
Post by: privatebydesign on July 15, 2013, 11:04:53 AM
This has been confusing for me for a long time thank you everyone for clarifying it.

Here's my new understanding.
• Physically the DOF does not change because your not changing the lens (ie. set up a shot,  switch a crop to a FF, and you'll just get a wider field of view but same DOF).
• But in practice it essentially does change (ie set up a shot, switch bodies, now move the came to have the same field of view, now the DOF of the crop camera photo will be larger. Same goes for not moving the camera and changing focal length).

If you change your physical aperture you change dof. If you change your subject magnification you change your dof. If you don't change either you don't change dof.

So both your points are valid.
Title: Re: How (and why) does sensor size change DOF?
Post by: ecka on July 15, 2013, 11:47:37 AM
This has been confusing for me for a long time thank you everyone for clarifying it.

Here's my new understanding.
• Physically the DOF does not change because your not changing the lens (ie. set up a shot,  switch a crop to a FF, and you'll just get a wider field of view but same DOF).
• But in practice it essentially does change (ie set up a shot, switch bodies, now move the came to have the same field of view, now the DOF of the crop camera photo will be larger. Same goes for not moving the camera and changing focal length).

Bingo! :)
Title: Re: How (and why) does sensor size change DOF?
Post by: Knut Skywalker on July 15, 2013, 01:30:52 PM
Well, thank you guys for the great explanation! I got confused because so many people stated that the DoF for a lens will be different when you use it on FF. The thing that changes the DoF is the distance to the subject to get the same framing. Basic answer to a basic question. :)
Title: Re: How (and why) does sensor size change DOF?
Post by: @!ex on July 15, 2013, 01:43:41 PM
picture is worth a thousand words
Title: Re: How (and why) does sensor size change DOF?
Post by: Vossie on July 15, 2013, 02:08:09 PM

Excellent comparison!

Oh dear,

Anybody that wants to argue the point really needs to read my two links, and get a background understanding on the CoC, circle of confusion.

The first thing you have to do when trying to understand this dof stuff is set a standard for your comparison. If we are going to assume a same sized reproduction, ie 8"x10" print or "fill screen" on the same monitor, and frame the image the same while shooting from the same place, you have to take everything into consideration.

Here is a comparison I did a while ago for another thread much like this one. It is a comparison based on the above criteria. The three images are identical in dof, noise, perspective, angle of view, etc etc.

If you read and understand the quote from Wikipedia I posted you will understand if you change your comparison criteria you will change the dof characteristics.
Title: Re: How (and why) does sensor size change DOF?
Post by: Etienne on July 15, 2013, 03:56:27 PM
DoF ~ focal length * aperture * subject distance
If you want to shoot the same picture using the same lens with both FF and crop sensor cameras, you need to be closer to the subject with FF camera to get the same framing and that's the only difference.

Good concise explanation!

I think of it like this:
A photographer must frame a shot. To get the same shot as a FF using the same lens on a crop camera, the photographer has to move backwards (by a factor of 1.6). Instead of 10 feet away, he must be 16 feet away. This increased focal distance increases the DOF of the shot.  Do the calculation here:   http://dofmaster.com/dofjs.html (http://dofmaster.com/dofjs.html)
Title: Re: How (and why) does sensor size change DOF?
Post by: Etienne on July 15, 2013, 04:20:32 PM
This has been confusing for me for a long time thank you everyone for clarifying it.

Here's my new understanding.
• Physically the DOF does not change because your not changing the lens (ie. set up a shot,  switch a crop to a FF, and you'll just get a wider field of view but same DOF).
• But in practice it essentially does change (ie set up a shot, switch bodies, now move the came to have the same field of view, now the DOF of the crop camera photo will be larger. Same goes for not moving the camera and changing focal length).

Yes.

Photographers frame shots. None of the ultra-technical mumbo-jumbo about "circle of confusion" and "DOF is a function of the lens" is helpful.

Using a 50mm lens:

Framing on a FF cam at 10 feet = Framing on a crop at 16 feet

BUT the extra focal distance necessary to frame the same shot on a crop camera causes the DOF to increase. In order to get the same shallow depth of field on the crop camera, the aperture has to be opened by 1.3 stops in comparison to the FF camera.

Prove it for yourself. Go to http://dofmaster.com/dofjs.html (http://dofmaster.com/dofjs.html) and calculate the DOF for ( these two examples will give the same fov framing of the scene):

Crop camera with 50mm lens at f=1.8 and distance 16 feet
FF camera with 50mm lens at f=2.8 and distance of 10 feet

These two examples result in the same DOF (2.1 feet total). The crop camera needs to increase the aperture by 1.3 stops in order to get the same DOF as the FF camera.

PS ... the effect of "circle of confusion" calculations for different sensors is completely swamped by the overwhelming effect of the need to stand further back to compose with a crop camera.
Title: Re: How (and why) does sensor size change DOF?
Post by: privatebydesign on July 15, 2013, 04:26:34 PM
DoF ~ focal length * aperture * subject distance
If you want to shoot the same picture using the same lens with both FF and crop sensor cameras, you need to be closer to the subject with FF camera to get the same framing and that's the only difference.

Good concise explanation!

I think of it like this:
A photographer must frame a shot. To get the same shot as a FF using the same lens on a crop camera, the photographer has to move backwards (by a factor of 1.6). Instead of 10 feet away, he must be 16 feet away. This increased focal distance increases the DOF of the shot.  Do the calculation here:   http://dofmaster.com/dofjs.html (http://dofmaster.com/dofjs.html)

It might be a concise explanation, but it is not good or accurate.

DOF, or CoC (they are entirely interchangeable), is a function of apparent aperture and subject magnification. Just those two. You can work out dof figures from just those two numbers. Subject magnification is a function of focal length and subject distance, as well as viewing distance and reproduction (print or screen) size.

When you put focal length and subject distance into a dof calculator all it is working out is the subject magnification on the sensor; it then needs the sensor size to work out the CoC for a given standard output, often an 8"x10" print viewed at 12".
Title: Re: How (and why) does sensor size change DOF?
Post by: Etienne on July 15, 2013, 04:38:48 PM
DoF ~ focal length * aperture * subject distance
If you want to shoot the same picture using the same lens with both FF and crop sensor cameras, you need to be closer to the subject with FF camera to get the same framing and that's the only difference.

Good concise explanation!

I think of it like this:
A photographer must frame a shot. To get the same shot as a FF using the same lens on a crop camera, the photographer has to move backwards (by a factor of 1.6). Instead of 10 feet away, he must be 16 feet away. This increased focal distance increases the DOF of the shot.  Do the calculation here:   http://dofmaster.com/dofjs.html (http://dofmaster.com/dofjs.html)

It might be a concise explanation, but it is not good or accurate.

DOF, or CoC (they are entirely interchangeable), is a function of apparent aperture and subject magnification. Just those two. You can work out dof figures from just those two numbers. Subject magnification is a function of focal length and subject distance, as well as viewing distance and reproduction (print or screen) size.

When you put focal length and subject distance into a dof calculator all it is working out is the subject magnification on the sensor; it then needs the sensor size to work out the CoC for a given standard output, often an 8"x10" print viewed at 12".

Wrong: the dof calculator also calculates the circle of confusion. http://dofmaster.com/dofjs.html (http://dofmaster.com/dofjs.html)

The technical mumbo-jumbo can be ignored. Crop factor cameras used to collect the same image as a FF camera will need to open the aperture by 1.3 stops in order to get the same DOF in the final image.

This is true regardless of whether you achieve the same field of view by moving the camera back by a factor of 1.6, or whether you use a shorter focal length (by a factor of 1.6, for Canon APS-C).

Circle of Confusion calculations won't make any difference at all. Partly because the effect is so small when comparing one real-world camera to another.
Title: Re: How (and why) does sensor size change DOF?
Post by: neuroanatomist on July 15, 2013, 05:23:53 PM
Wrong: the dof calculator also calculates the circle of confusion. http://dofmaster.com/dofjs.html (http://dofmaster.com/dofjs.html)

The technical mumbo-jumbo can be ignored.

Sorry, but then I suggest that you just ignore it, instead of calling others' correct statements wrong based on your misunderstanding.

FYI, DoFMaster doesn't calculate CoC, it assigns a standard value based on sensor size. It uses that assigned value to calculate DoF.
Title: Re: How (and why) does sensor size change DOF?
Post by: Marsu42 on July 15, 2013, 05:31:19 PM
Last not least, note that if people rave about thin dof they often mean "strong background blur" except if you like the "only the nose in focus" type shots, and same thing here: bokeh also strongly depends on focal length and object/background distance relationship.
Except that bokeh really refers to the quality of the OOF blur, independent of quantity.  But maybe that's a story for another day.  ;)

Thanks for the hint, you are correct, even trusty Wikipedia says so (though you've probably written the article there :-)).
Title: Re: How (and why) does sensor size change DOF?
Post by: privatebydesign on July 15, 2013, 08:10:02 PM

The technical mumbo-jumbo can be ignored. ..................

Circle of Confusion calculations won't make any difference at all. Partly because the effect is so small when comparing one real-world camera to another.

A common CoC figure for 135 format sensor is 0.029mm, divide that by 1.6 and you get? Voila, 0.018mm, the CoC for APS-C. if you wanted to ignore the difference in CoC, that is the same magnitude as focal length, aperture and noise, then you might as well ignore all of it!

You can't ignore the "technical mumbo-jumbo" in answering a technical question.

Now if you did want to ignore CoC differences you could, but your crop camera print (or on screen) could only be 40% as big as the ff print. If you were looking at an 8"x10" ff print you could only compare that to a 5"x6.25" crop print. Or a 12"x16" crop print would have the same CoC characteristics as a ff print 19"x26", quite a difference to my mind.
Title: Re: How (and why) does sensor size change DOF?
Post by: MrFotoFool on July 15, 2013, 10:22:50 PM
I was hoping this thread would answer the question for me too, but I would have been better off not reading it.  Now I am in the circle of confusion.

If I am understanding the consensus, the only difference is due to the need to back up or use a wider angle lens in APS-C to get the same coverage.  If you have a FF and APS-C camera at the same position and same lens and aperture, the depth of field will be the same (even though the APS-C shot will be cropped tighter).

I am not sure I agree with this (but I very well could be wrong).  My experience is based on shooting through zoo fences with my cousin on APS-C and me on full frame.  I could swear there were times we had the same lens length and aperture and yet I could blur out the fence and he could not.  I have heard that full frame cameras have a shallower depth of field and this experience seems to confirm that.  Am I just imaging things?
Title: Re: How (and why) does sensor size change DOF?
Post by: neuroanatomist on July 15, 2013, 10:42:30 PM
I am not sure I agree with this (but I very well could be wrong).  My experience is based on shooting through zoo fences with my cousin on APS-C and me on full frame.  I could swear there were times we had the same lens length and aperture and yet I could blur out the fence and he could not.  I have heard that full frame cameras have a shallower depth of field and this experience seems to confirm that.  Am I just imaging things?

Sorry, but probably, yes. If you were, in fact, using the same lens and aperture and not changing magnification (distance), and were the same distance from the fence, the blur would be equivalent.
Title: Re: How (and why) does sensor size change DOF?
Post by: bdunbar79 on July 15, 2013, 11:22:18 PM
DoF ~ focal length * aperture * subject distance
If you want to shoot the same picture using the same lens with both FF and crop sensor cameras, you need to be closer to the subject with FF camera to get the same framing and that's the only difference.

Good concise explanation!

I think of it like this:
A photographer must frame a shot. To get the same shot as a FF using the same lens on a crop camera, the photographer has to move backwards (by a factor of 1.6). Instead of 10 feet away, he must be 16 feet away. This increased focal distance increases the DOF of the shot.  Do the calculation here:   http://dofmaster.com/dofjs.html (http://dofmaster.com/dofjs.html)

It might be a concise explanation, but it is not good or accurate.

DOF, or CoC (they are entirely interchangeable), is a function of apparent aperture and subject magnification. Just those two. You can work out dof figures from just those two numbers. Subject magnification is a function of focal length and subject distance, as well as viewing distance and reproduction (print or screen) size.

When you put focal length and subject distance into a dof calculator all it is working out is the subject magnification on the sensor; it then needs the sensor size to work out the CoC for a given standard output, often an 8"x10" print viewed at 12".

Wrong: the dof calculator also calculates the circle of confusion. http://dofmaster.com/dofjs.html (http://dofmaster.com/dofjs.html)

The technical mumbo-jumbo can be ignored. Crop factor cameras used to collect the same image as a FF camera will need to open the aperture by 1.3 stops in order to get the same DOF in the final image.

This is true regardless of whether you achieve the same field of view by moving the camera back by a factor of 1.6, or whether you use a shorter focal length (by a factor of 1.6, for Canon APS-C).

Circle of Confusion calculations won't make any difference at all. Partly because the effect is so small when comparing one real-world camera to another.

Title: Re: How (and why) does sensor size change DOF?
Post by: shashinkaman on July 15, 2013, 11:41:47 PM
As per usual: "full of sound and fury..."  ;D No need to get your panties in a twist, but do you CR people actually take pictures too, or just blablabla your days away???  8) How about posting some (good!) shots to prove your point? Especially you Neuro, you are always acting like you are the most knowledgable photographer on CR, but we haven't seen much of your great volume of work now haven't we? How about accepting my challenge and go out somewhere, shoot a number of pictures to prove your theory (what ever that was) and impress us with your work instead of your words...?
Title: Re: How (and why) does sensor size change DOF?
Post by: bdunbar79 on July 15, 2013, 11:49:09 PM
As per usual: "full of sound and fury..."  ;D No need to get your panties in a twist, but do you CR people actually take pictures too, or just blablabla your days away???  8) How about posting some (good!) shots to prove your point? Especially you Neuro, you are always acting like you are the most knowledgable photographer on CR, but we haven't seen much of your great volume of work now haven't we? How about accepting my challenge and go out somewhere, shoot a number of pictures to prove your theory (what ever that was) and impress us with your work instead of your words...?

It's actually not neuro's theory.  The question was, "does sensor size affect DOF?" (admittedly highly evolved since the OP's question).  There is only one correct and objective answer, and the answer is YES.  What more needs to be said?  At least he is trying to educate and offer an explanation.  This concept is not some unknown or magical theory.  Anyone knows sensor size affects DOF.

What is highly ironic, is that you refer to the thread as "you CR people" wasting time when in fact you yourself have contributed absolutely nothing to the thread.  I highly doubt neuro, or anyone really for that matter, cares about your challenge and owes absolutely nothing to you.

With that aside, DOF is affected by sensor size.  Ok?
Title: Re: How (and why) does sensor size change DOF?
Post by: BozillaNZ on July 16, 2013, 12:43:19 AM
How do you define 'DOF'?

Q1. If you shoot photo A using FF+50, then photo B using APS+35, at same F number DoF of photo B > photo A

Q2. If you shoot a photo A, then crop the border out leaving a smaller photo B, magnify it back to original size, DoF of photo B < A, but since the framing has changed, it's not the same photo anymore.

And that's it. DoF on two different format has two trends fighting against each other. One tends to decrease DoF (entrance pupil size), another tends to increase it (magnification or CoC). So here's the answer:

Answer 1. When comparing using the same Angle of View (effective focal length), larger sensor always has less DoF.

Answer 2. When comparing using different Angle of View, like comparing two different photos, it DOESN'T MAKE SENSE.

It seems most of the arguments and 'confusions' are around point 2, which is not a valid argument at all. Different Angle of View can never give you the same photo, you are comparing apple to orange.

Title: Re: How (and why) does sensor size change DOF?
Post by: MrFotoFool on July 16, 2013, 02:05:24 AM
The question was, "does sensor size affect DOF?" (admittedly highly evolved since the OP's question).  There is only one correct and objective answer, and the answer is YES.

Actually what I hear people saying is the answer is NO.
Title: Re: How (and why) does sensor size change DOF?
Post by: verysimplejason on July 16, 2013, 02:38:11 AM
Here's an explanation on DOF and sensor size.  There's also a calculator for this.

http://www.cambridgeincolour.com/tutorials/digital-camera-sensor-size.htm (http://www.cambridgeincolour.com/tutorials/digital-camera-sensor-size.htm)
Title: Re: How (and why) does sensor size change DOF?
Post by: Pi on July 16, 2013, 02:59:26 AM
Speaking about sensor size changing the DOF is a bit misleading. Do we keep everything else the same? This is actually impossible. You cannot keep the AOV and the FL the same. If we just swap the bodies, without changing (physically) anything else, smaller sensors have less DOF.

For the same AOV and same f/stop, larger sensors with the corresponding lenses have less DOF because the "physical aperture" is larger. For example, 80/2>50/2. There is no rule saying you must shoot at the same f-stops with both sensors, and if you shoot with equivalents ones (like 80/3.2 vs. 50/2) DOF is the same. That means "faster" lenses for the smaller sensor. They do not always exists, but sometimes, they do. For example, the m43 system has f/2 zooms, eq. to f/4 ones. They also have a f/0.95 prime, eq. to an f/2 one. But they do not have a match for f/1.4 on FF.

Bottom line: it is not the sensor size, it is the lens and the sensor but lenses with less DOF for larger sensors are easier to make, more common, cost less, and resolve more.
Title: Re: How (and why) does sensor size change DOF?
Post by: Wild on July 16, 2013, 03:52:52 AM
Depth of Field refers to the plane of focus within a photograph. A photo with a large depth of field might have much of the photo in focus, whereas a photo with a shallow depth of field might only have a few inches in focus.

The definition of "Depth of field" that you care about, is a collaboration between the sensor size, the focal length, and the aperture used to capture an image. Given the same focal length, with the same aperture, with the subject of focus the same distance away - a larger sensor will always have the shallower perceived depth of field. The actual depth of field is the same, but the narrower field of view caused by a smaller sensors' crop factor makes it seem as though the background is less blurred.

Put another way, if you were to frame a subject equally with a large sensor and a small sensor. The full frame would have to be much closer to the subject to have equal framing. Being closer to the subject causes the full frame's plane of focus to be shallower, therefore creating more blur in the background compared to the smaller sensor.

That's the key to the perceived depth of field advantage of full frame. Capturing a larger scene with a bigger sensor forces you to be closer to the subject to maintain the same framing as a small sensor, thereby shrinking the depth of field plane, and creating more background blur.

Everybody arguing about this seemingly simple, yet oddly complex question are forgetting that this started out as an innocent request for knowledge. We shouldn't be so quick to jump all over each others' cases - it only makes people hesitant to post thinking they'll be attacked with one misplaced word.

Title: Re: How (and why) does sensor size change DOF?
Post by: ecka on July 16, 2013, 04:49:52 AM
How do you define 'DOF'?

Q1. If you shoot photo A using FF+50, then photo B using APS+35, at same F number DoF of photo B > photo A

Q2. If you shoot a photo A, then crop the border out leaving a smaller photo B, magnify it back to original size, DoF of photo B < A, but since the framing has changed, it's not the same photo anymore.

And that's it. DoF on two different format has two trends fighting against each other. One tends to decrease DoF (entrance pupil size), another tends to increase it (magnification or CoC). So here's the answer:

Answer 1. When comparing using the same Angle of View (effective focal length), larger sensor always has less DoF.

Answer 2. When comparing using different Angle of View, like comparing two different photos, it DOESN'T MAKE SENSE.

It seems most of the arguments and 'confusions' are around point 2, which is not a valid argument at all. Different Angle of View can never give you the same photo, you are comparing apple to orange.

Q2. If you shoot a photo A, then crop the border out leaving a smaller photo B, magnify it back to original size, then in relativity to reality DoF A = DoF B, but in relativity to dimensions of the photograph DoF A < DoF B, because you are not getting closer, you are magnifying it as well as the DoF.
Title: Re: How (and why) does sensor size change DOF?
Post by: endiendo on July 16, 2013, 05:22:46 AM
Look for a pdf named "Canon-Full-Frame-CMOS-White-Paper"..  It's very well explained in it..
Title: Re: How (and why) does sensor size change DOF?
Post by: BozillaNZ on July 16, 2013, 05:31:56 AM
Q2. If you shoot a photo A, then crop the border out leaving a smaller photo B, magnify it back to original size, then in relativity to reality DoF A = DoF B, but in relativity to dimensions of the photograph DoF A < DoF B, because you are not getting closer, you are magnifying it as well as the DoF.

No need to cross my text just because you don't agree with me. Photo is always relative to dimensions of the output, there is no relative to 'reality' to speak of, otherwise your are just muddying the water. When you are comparing two photographs, you compare them at the same output size, otherwise the comparison is just wrong.

"Yeah, put those two photo side by side, B has 2 times larger blur circle in the background, but when you make photo B 2 times smaller, the blur will look just the same!" Well, you are essentially manipulating objectivity to make it suit your theory.
Title: Re: How (and why) does sensor size change DOF?
Post by: BozillaNZ on July 16, 2013, 05:48:48 AM
Image 1 FF, with various blur circles

Image 2 M4/3, with the same image cropped 2x in the center

If you measure them, the blur circles in M4/3 image are twice as larger as in FF image, hence it's DoF is smaller. If you don't agree with this, then telephoto provides shallower DoF should also be false to you, since "zoom in" in optical and digital terms are just the same. And shooting a 50mm f1.4 on M4/3 would be similar to shooting 100mm f2.8 on FF, so those two images can also be interpreted as:

Image 1 FF, 50 f1.4

Image 2 FF, 100 f2.8

Now it becomes interesting to ask: which one is shallower?  ;D (the answer: it depends.)
Title: Re: How (and why) does sensor size change DOF?
Post by: ecka on July 16, 2013, 05:52:52 AM
Q2. If you shoot a photo A, then crop the border out leaving a smaller photo B, magnify it back to original size, then in relativity to reality DoF A = DoF B, but in relativity to dimensions of the photograph DoF A < DoF B, because you are not getting closer, you are magnifying it as well as the DoF.

No need to cross my text just because you don't agree with me. Photo is always relative to dimensions of the output, there is no relative to 'reality' to speak of, otherwise your are just muddying the water. When you are comparing two photographs, you compare them at the same output size, otherwise the comparison is just wrong.

"Yeah, put those two photo side by side, B has 2 times larger blur circle in the background, but when you make photo B 2 times smaller, the blur will look just the same!" Well, you are essentially manipulating objectivity to make it suit your theory.

I'm just stating facts. Blur circles ≠ DoF.
DoF A is shallower in both cases, except when you are measuring it in blur circles. By your logic: P&S camera has the biggest blur circles (sometimes they don't fit inside the image :) ), therefore it produces the thinnest DoF when compared with the same focal length lens on a DSLR. This is wrong in all theories, not just mine.
Title: Re: How (and why) does sensor size change DOF?
Post by: BozillaNZ on July 16, 2013, 05:54:11 AM
Q2. If you shoot a photo A, then crop the border out leaving a smaller photo B, magnify it back to original size, then in relativity to reality DoF A = DoF B, but in relativity to dimensions of the photograph DoF A < DoF B, because you are not getting closer, you are magnifying it as well as the DoF.

No need to cross my text just because you don't agree with me. Photo is always relative to dimensions of the output, there is no relative to 'reality' to speak of, otherwise your are just muddying the water. When you are comparing two photographs, you compare them at the same output size, otherwise the comparison is just wrong.

"Yeah, put those two photo side by side, B has 2 times larger blur circle in the background, but when you make photo B 2 times smaller, the blur will look just the same!" Well, you are essentially manipulating objectivity to make it suit your theory.

I'm just stating facts. Blur circles ≠ DoF.
DoF A is shallower in both cases, except when you are measuring it in blur circles. By your logic: P&S camera has the biggest blur circles (sometimes thei don't fit inside the image :) ), therefore it produces the thinnest DoF when compared with the same focal length lens on a DSLR. This is wrong in all theories, not just mine.

"thinnest DoF when compared with the same focal length" < This, if you can somehow manage to put a 100mm lens on a P&S, it gives you a huge telephoto equivalence, then DoF will also be a lot thinner than when the lens is mounted on a DSLR. Think about it...
Title: Re: How (and why) does sensor size change DOF?
Post by: insanitybeard on July 16, 2013, 05:56:18 AM
As per usual: "full of sound and fury..."  ;D No need to get your panties in a twist, but do you CR people actually take pictures too, or just blablabla your days away???  8) How about posting some (good!) shots to prove your point? Especially you Neuro, you are always acting like you are the most knowledgable photographer on CR, but we haven't seen much of your great volume of work now haven't we? How about accepting my challenge and go out somewhere, shoot a number of pictures to prove your theory (what ever that was) and impress us with your work instead of your words...?

Perhaps if you clicked on the flickr link at the bottom of Neuro's profile you would find the body of pictures you seek?

What a stupid comment to make. Perhaps you should check your facts before making such remarks.
Title: Re: How (and why) does sensor size change DOF?
Post by: ecka on July 16, 2013, 06:02:40 AM
Q2. If you shoot a photo A, then crop the border out leaving a smaller photo B, magnify it back to original size, then in relativity to reality DoF A = DoF B, but in relativity to dimensions of the photograph DoF A < DoF B, because you are not getting closer, you are magnifying it as well as the DoF.

No need to cross my text just because you don't agree with me. Photo is always relative to dimensions of the output, there is no relative to 'reality' to speak of, otherwise your are just muddying the water. When you are comparing two photographs, you compare them at the same output size, otherwise the comparison is just wrong.

"Yeah, put those two photo side by side, B has 2 times larger blur circle in the background, but when you make photo B 2 times smaller, the blur will look just the same!" Well, you are essentially manipulating objectivity to make it suit your theory.

I'm just stating facts. Blur circles ≠ DoF.
DoF A is shallower in both cases, except when you are measuring it in blur circles. By your logic: P&S camera has the biggest blur circles (sometimes thei don't fit inside the image :) ), therefore it produces the thinnest DoF when compared with the same focal length lens on a DSLR. This is wrong in all theories, not just mine.

"thinnest DoF when compared with the same focal length" < This, if you can somehow manage to put a 100mm lens on a P&S, it gives you a huge telephoto equivalence, then DoF will also be a lot thinner than when the lens is mounted on a DSLR. Think about it...

Yes, you can put a 100mm lens on a P&S (try Pentax Q or Nikon 1) and you are still wrong. I always measure DoF in relativity to reality, not "bokeh balls". :)
Title: Re: How (and why) does sensor size change DOF?
Post by: BozillaNZ on July 16, 2013, 06:07:49 AM
Yes, you can put a 100mm lens on a P&S (try Pentax Q or Nikon 1) and you are still wrong. I always measure DoF in relativity to reality, not "bokeh balls". :)

Due to different standards, I still call this comparison apples to oranges.

Result: When talking about format affecting DoF, always compare same angle of view, or effective focal length, since comparing different angle of view doesn't make sense.

We are still in disagreement but that's okay.
Title: Re: How (and why) does sensor size change DOF?
Post by: ecka on July 16, 2013, 06:30:15 AM
Yes, you can put a 100mm lens on a P&S (try Pentax Q or Nikon 1) and you are still wrong. I always measure DoF in relativity to reality, not "bokeh balls". :)

Due to different standards, I still call this comparison apples to oranges.

Result: When talking about format affecting DoF, always compare same angle of view, or effective focal length, since comparing different angle of view doesn't make sense.

We are still in disagreement but that's okay.

These are small apples vs big apples of the same taste :)

When comparing different formats using the same lens at the same distance and aperture (different FoV) - DoF is the same.
When comparing different formats using different but equivalent lenses and apertures at the same distance (like APSC+50/1.8 vs FF+80/2.8, same FoV) - DoF is the same.
Cropping the image doesn't change the DoF.

When comparing different formats using the same lens and aperture at equivalent distance (same FoV) - FF DoF is thinner.
When comparing different formats using different but equivalent lenses at the same distance and aperture (like APSC+85/2 vs FF+135/2, same FoV) - FF DoF is thinner.

Title: Re: How (and why) does sensor size change DOF?
Post by: BozillaNZ on July 16, 2013, 07:25:50 AM
When comparing different formats using the same lens and aperture at equivalent distance (same FoV) -

That's just not possible. It is not possible to have same lens (assume prime) mounted on different sensor format and still achieve same FoV. Physics doesn't work like that.

If by 'same FoV' you mean same subject framing, then background would have different magnification. That's my point, different perspective can't be compared.

Also from your above post, you seem to indicate that under all circumstances FF will always have equal or shallower DoF, I and a lot others couldn't agree on that.
Title: Re: How (and why) does sensor size change DOF?
Post by: ecka on July 16, 2013, 08:06:21 AM
When comparing different formats using the same lens and aperture at equivalent distance (same FoV) -

That's just not possible. It is not possible to have same lens (assume prime) mounted on different sensor format and still achieve same FoV. Physics doesn't work like that.

If by 'same FoV' you mean same subject framing, then background would have different magnification. That's my point, different perspective can't be compared.

Yes, same FoV means same angle and, of course, the perspective in some cases will be different.

Quote
Also from your above post, you seem to indicate that under all circumstances FF will always have equal or shallower DoF, I and a lot others couldn't agree on that.

That is correct and the whole lot of others is misinformed.
Title: Re: How (and why) does sensor size change DOF?
Post by: Knut Skywalker on July 16, 2013, 08:54:43 AM
Wow...this became a way bigger discussion than i intented it to be. :o

So if i got everything right it is like that:

Same focal length + same aperture + same distance to subject on different formats =  different FoV but with same same DoF. And that makes total sense to me because the lens projects the same image as before but on a smaller area to capture it.

And same focal length + same aperture + same object framing (which means bigger distance to subject on smaller formats) = bigger DoF on small formats because the focal distance is further away and smaller DoF on bigger formats because the focal distance is closer to MFD.

I hope my english is good enouh so everybody undertood what i meant...  :-[

Greetings from Germany,
Knut Skywalker
Title: Re: How (and why) does sensor size change DOF?
Post by: ecka on July 16, 2013, 09:00:37 AM
Wow...this became a way bigger discussion than i intented it to be. :o

So if i got everything right it is like that:

Same focal length + same aperture + same distance to subject on different formats =  different FoV but with same same DoF. And that makes total sense to me because the lens projects the same image as before but on a smaller area to capture it.

And same focal length + same aperture + same object framing (which means bigger distance to subject on smaller formats) = bigger DoF on small formats because the focal distance is further away and smaller DoF on bigger formats because the focal distance is closer to MFD.

I hope my english is good enouh so everybody undertood what i meant...  :-[

Greetings from Germany,
Knut Skywalker

Yes, you've got it right.
Title: Re: How (and why) does sensor size change DOF?
Post by: privatebydesign on July 16, 2013, 09:42:58 AM
Wow...this became a way bigger discussion than i intented it to be. :o

So if i got everything right it is like that:

Same focal length + same aperture + same distance to subject on different formats =  different FoV but with same same DoF. And that makes total sense to me because the lens projects the same image as before but on a smaller area to capture it.

And same focal length + same aperture + same object framing (which means bigger distance to subject on smaller formats) = bigger DoF on small formats because the focal distance is further away and smaller DoF on bigger formats because the focal distance is closer to MFD.

I hope my english is good enouh so everybody undertood what i meant...  :-[

Greetings from Germany,
Knut Skywalker

Yes, you've got it right.

No, that is not correct.

"Same focal length + same aperture + same distance to subject on different formats =  different FoV but with same same DoF."

That scenario, assuming you are comparing same sized reproductions (print or screen), results in less DoF from the crop camera because it is has a smaller CoC. Think of it like this, you have to enlarge the crop cameras image 2.5 times more (by area) than the ff one, bigger reproduction ratio = less dof. Don't forget any detail of the crop camera image is reproduced bigger than the same detail from the ff image on a same sized print (or screen).

IF, using your above scenario, you compared two prints from the different sensors where the details of the subject were the same size, so the crop camera print would be 40% the size of the ff print, then the dof would be identical.

You cannot remove reproduction size from the DoF calculation, DoF calculators assume a base standard, often an 8"x10" print viewed at 12", if you compare two same sized prints from different sized sensors then the smaller sensor has been enlarged more.

This is all covered and explained in my first reply, the second post, on page one. "If pictures are taken from the same distance using the same f-number, same focal length, and the final images are the same size, the smaller format has less DOF."
Title: Re: How (and why) does sensor size change DOF?
Post by: J.R. on July 16, 2013, 09:49:47 AM
Wow...this became a way bigger discussion than i intented it to be. :o

So if i got everything right it is like that:

Same focal length + same aperture + same distance to subject on different formats =  different FoV but with same same DoF. And that makes total sense to me because the lens projects the same image as before but on a smaller area to capture it.

And same focal length + same aperture + same object framing (which means bigger distance to subject on smaller formats) = bigger DoF on small formats because the focal distance is further away and smaller DoF on bigger formats because the focal distance is closer to MFD.

I hope my english is good enouh so everybody undertood what i meant...  :-[

Greetings from Germany,
Knut Skywalker

Yes, you've got it right.

No, that is not correct.

"Same focal length + same aperture + same distance to subject on different formats =  different FoV but with same same DoF."

That scenario, assuming you are comparing same sized reproductions (print or screen), results in less DoF from the crop camera because it is has a smaller CoC. Think of it like this, you have to enlarge the crop cameras image 2.5 times more (by area) than the ff one, bigger reproduction ratio = less dof. Don't forget any detail of the crop camera image is reproduced bigger than the same detail from the ff image on a same sized print (or screen).

IF, using your above scenario, you compared two prints from the different sensors where the details of the subject were the same size, so the crop camera print would be 40% the size of the ff print, then the dof would be identical.

You cannot remove reproduction size from the DoF calculation, DoF calculators assume a base standard, often an 8"x10" print viewed at 12", if you compare two same sized prints from different sized sensors then the smaller sensor has been enlarged more.

This is all covered and explained in my first reply, the second post, on page one. "If pictures are taken from the same distance using the same f-number, same focal length, and the final images are the same size, the smaller format has less DOF."

Quite correct. Canon itself uses a COC 0.035mm in DOF calculations for FF. On APS-C the image must be enlarged more to produce a 7x5 inch print, which means a smaller COC is needed and hence for APS-C, Canon uses a COC of 0.019mm in its calculations.
Title: Re: How (and why) does sensor size change DOF?
Post by: ecka on July 16, 2013, 10:08:06 AM
Wow...this became a way bigger discussion than i intented it to be. :o

So if i got everything right it is like that:

Same focal length + same aperture + same distance to subject on different formats =  different FoV but with same same DoF. And that makes total sense to me because the lens projects the same image as before but on a smaller area to capture it.

And same focal length + same aperture + same object framing (which means bigger distance to subject on smaller formats) = bigger DoF on small formats because the focal distance is further away and smaller DoF on bigger formats because the focal distance is closer to MFD.

I hope my english is good enouh so everybody undertood what i meant...  :-[

Greetings from Germany,
Knut Skywalker

Yes, you've got it right.

No, that is not correct.

"Same focal length + same aperture + same distance to subject on different formats =  different FoV but with same same DoF."

That scenario, assuming you are comparing same sized reproductions (print or screen), results in less DoF from the crop camera because it is has a smaller CoC. Think of it like this, you have to enlarge the crop cameras image 2.5 times more (by area) than the ff one, bigger reproduction ratio = less dof. Don't forget any detail of the crop camera image is reproduced bigger than the same detail from the ff image on a same sized print (or screen).

IF, using your above scenario, you compared two prints from the different sensors where the details of the subject were the same size, so the crop camera print would be 40% the size of the ff print, then the dof would be identical.

You cannot remove reproduction size from the DoF calculation, DoF calculators assume a base standard, often an 8"x10" print viewed at 12", if you compare two same sized prints from different sized sensors then the smaller sensor has been enlarged more.

This is all covered and explained in my first reply, the second post, on page one. "If pictures are taken from the same distance using the same f-number, same focal length, and the final images are the same size, the smaller format has less DOF."

Quite correct. Canon itself uses a COC 0.035mm in DOF calculations for FF. On APS-C the image must be enlarged more to produce a 7x5 inch print, which means a smaller COC is needed and hence for APS-C, Canon uses a COC of 0.019mm in its calculations.

So, in your reality, if you print the same picture in two different sizes, the bigger one will have less DoF? :D
Good lord... I'm wasting my time here  ???
Same logic - there is a magical print size which makes your P&S images look like they were shot using a FF camera? :D ... and the next one is even better?
Title: Re: How (and why) does sensor size change DOF?
Post by: privatebydesign on July 16, 2013, 10:18:30 AM
Wow...this became a way bigger discussion than i intented it to be. :o

So if i got everything right it is like that:

Same focal length + same aperture + same distance to subject on different formats =  different FoV but with same same DoF. And that makes total sense to me because the lens projects the same image as before but on a smaller area to capture it.

And same focal length + same aperture + same object framing (which means bigger distance to subject on smaller formats) = bigger DoF on small formats because the focal distance is further away and smaller DoF on bigger formats because the focal distance is closer to MFD.

I hope my english is good enouh so everybody undertood what i meant...  :-[

Greetings from Germany,
Knut Skywalker

Yes, you've got it right.

No, that is not correct.

"Same focal length + same aperture + same distance to subject on different formats =  different FoV but with same same DoF."

That scenario, assuming you are comparing same sized reproductions (print or screen), results in less DoF from the crop camera because it is has a smaller CoC. Think of it like this, you have to enlarge the crop cameras image 2.5 times more (by area) than the ff one, bigger reproduction ratio = less dof. Don't forget any detail of the crop camera image is reproduced bigger than the same detail from the ff image on a same sized print (or screen).

IF, using your above scenario, you compared two prints from the different sensors where the details of the subject were the same size, so the crop camera print would be 40% the size of the ff print, then the dof would be identical.

You cannot remove reproduction size from the DoF calculation, DoF calculators assume a base standard, often an 8"x10" print viewed at 12", if you compare two same sized prints from different sized sensors then the smaller sensor has been enlarged more.

This is all covered and explained in my first reply, the second post, on page one. "If pictures are taken from the same distance using the same f-number, same focal length, and the final images are the same size, the smaller format has less DOF."

Quite correct. Canon itself uses a COC 0.035mm in DOF calculations for FF. On APS-C the image must be enlarged more to produce a 7x5 inch print, which means a smaller COC is needed and hence for APS-C, Canon uses a COC of 0.019mm in its calculations.

So, in your reality, if you print the same picture in two different sizes, the bigger one will have less DoF? :D
Good lord... I'm wasting my time here  ???
Same logic - there is a magical print size which makes your P&S images look like they were shot using a FF camera? :D

Yes that is the reality I live in, unbeknown to you it is also the reality you live in, ignorance is bliss, you are wasting everybody's time here.....

Reproduction size and viewing distances are fundamental to DoF calculations, you cannot work out DoF figures without knowing how big your print will be and the viewing distance, as I keep saying, DoF calculators often work to the standard of an 8"x10" print viewed at 12".

Read about CoC, you know that "technical mumbo-jumbo" "you can ignore", well it turns out you can't ignore it if you want to understand the answer to the OP's question.
Title: Re: How (and why) does sensor size change DOF?
Post by: ecka on July 16, 2013, 10:44:28 AM
Wow...this became a way bigger discussion than i intented it to be. :o

So if i got everything right it is like that:

Same focal length + same aperture + same distance to subject on different formats =  different FoV but with same same DoF. And that makes total sense to me because the lens projects the same image as before but on a smaller area to capture it.

And same focal length + same aperture + same object framing (which means bigger distance to subject on smaller formats) = bigger DoF on small formats because the focal distance is further away and smaller DoF on bigger formats because the focal distance is closer to MFD.

I hope my english is good enouh so everybody undertood what i meant...  :-[

Greetings from Germany,
Knut Skywalker

Yes, you've got it right.

No, that is not correct.

"Same focal length + same aperture + same distance to subject on different formats =  different FoV but with same same DoF."

That scenario, assuming you are comparing same sized reproductions (print or screen), results in less DoF from the crop camera because it is has a smaller CoC. Think of it like this, you have to enlarge the crop cameras image 2.5 times more (by area) than the ff one, bigger reproduction ratio = less dof. Don't forget any detail of the crop camera image is reproduced bigger than the same detail from the ff image on a same sized print (or screen).

IF, using your above scenario, you compared two prints from the different sensors where the details of the subject were the same size, so the crop camera print would be 40% the size of the ff print, then the dof would be identical.

You cannot remove reproduction size from the DoF calculation, DoF calculators assume a base standard, often an 8"x10" print viewed at 12", if you compare two same sized prints from different sized sensors then the smaller sensor has been enlarged more.

This is all covered and explained in my first reply, the second post, on page one. "If pictures are taken from the same distance using the same f-number, same focal length, and the final images are the same size, the smaller format has less DOF."

Quite correct. Canon itself uses a COC 0.035mm in DOF calculations for FF. On APS-C the image must be enlarged more to produce a 7x5 inch print, which means a smaller COC is needed and hence for APS-C, Canon uses a COC of 0.019mm in its calculations.

So, in your reality, if you print the same picture in two different sizes, the bigger one will have less DoF? :D
Good lord... I'm wasting my time here  ???
Same logic - there is a magical print size which makes your P&S images look like they were shot using a FF camera? :D

Yes that is the reality I live in, unbeknown to you it is also the reality you live in, ignorance is bliss, you are wasting everybody's time here.....

Reproduction size and viewing distances are fundamental to DoF calculations, you cannot work out DoF figures without knowing how big your print will be and the viewing distance, as I keep saying, DoF calculators often work to the standard of an 8"x10" print viewed at 12".

Read about CoC, you know that "technical mumbo-jumbo" "you can ignore", well it turns out you can't ignore it if you want to understand the answer to the OP's question.

The CoC is not about DoF. When there are 3 parts in the image - sharp (DoF), blur (OOF) and "not sure", the CoC is about the "not sure" part.

Don't try to bend the spoon, that's impossible, because there is no spoon.
Title: Re: How (and why) does sensor size change DOF?
Post by: J.R. on July 16, 2013, 10:46:19 AM
Wow...this became a way bigger discussion than i intented it to be. :o

So if i got everything right it is like that:

Same focal length + same aperture + same distance to subject on different formats =  different FoV but with same same DoF. And that makes total sense to me because the lens projects the same image as before but on a smaller area to capture it.

And same focal length + same aperture + same object framing (which means bigger distance to subject on smaller formats) = bigger DoF on small formats because the focal distance is further away and smaller DoF on bigger formats because the focal distance is closer to MFD.

I hope my english is good enouh so everybody undertood what i meant...  :-[

Greetings from Germany,
Knut Skywalker

Yes, you've got it right.

No, that is not correct.

"Same focal length + same aperture + same distance to subject on different formats =  different FoV but with same same DoF."

That scenario, assuming you are comparing same sized reproductions (print or screen), results in less DoF from the crop camera because it is has a smaller CoC. Think of it like this, you have to enlarge the crop cameras image 2.5 times more (by area) than the ff one, bigger reproduction ratio = less dof. Don't forget any detail of the crop camera image is reproduced bigger than the same detail from the ff image on a same sized print (or screen).

IF, using your above scenario, you compared two prints from the different sensors where the details of the subject were the same size, so the crop camera print would be 40% the size of the ff print, then the dof would be identical.

You cannot remove reproduction size from the DoF calculation, DoF calculators assume a base standard, often an 8"x10" print viewed at 12", if you compare two same sized prints from different sized sensors then the smaller sensor has been enlarged more.

This is all covered and explained in my first reply, the second post, on page one. "If pictures are taken from the same distance using the same f-number, same focal length, and the final images are the same size, the smaller format has less DOF."

Quite correct. Canon itself uses a COC 0.035mm in DOF calculations for FF. On APS-C the image must be enlarged more to produce a 7x5 inch print, which means a smaller COC is needed and hence for APS-C, Canon uses a COC of 0.019mm in its calculations.

So, in your reality, if you print the same picture in two different sizes, the bigger one will have less DoF? :D
Good lord... I'm wasting my time here  ???
Same logic - there is a magical print size which makes your P&S images look like they were shot using a FF camera? :D ... and the next one is even better?

This reality and comes from Canon directly and if instead of pointless arguing if you undertook a little bit of research, you may learn something. At the cost of wasting my time, I point you to these "official" Canon links -

http://cpn.canon-europe.com/content/education/technical/depth_of_field_calculator.do (http://cpn.canon-europe.com/content/education/technical/depth_of_field_calculator.do)
http://cpn.canon-europe.com/content/education/infobank/depth_of_field/depth_of_field.do (http://cpn.canon-europe.com/content/education/infobank/depth_of_field/depth_of_field.do)

Have a nice day
Title: Re: How (and why) does sensor size change DOF?
Post by: Etienne on July 16, 2013, 11:01:37 AM
Pointless discussion.

In practice, if you want to achieve the same depth of field on a crop as FF, you need to open the aperture on the crop camera by 1.3 stops.

Now ... let the confusion of circulars begin
Title: Re: How (and why) does sensor size change DOF?
Post by: insanitybeard on July 16, 2013, 11:04:27 AM
Pointless discussion.

In practice, if you want to achieve the same depth of field on a crop as FF, you need to open the aperture on the crop camera by 1.3 stops.

Now ... let the confusion of circulars begin

How is it a pointless discussion when the original question, explicitly was : 'How (and why) does sensor size change DOF?'
Title: Re: How (and why) does sensor size change DOF?
Post by: privatebydesign on July 16, 2013, 11:07:00 AM

The CoC is not about DoF. When there are 3 parts in the image - sharp (DoF), blur (OOF) and "not sure", the CoC is about the "not sure" part.

I am sorry, you are so incorrect about so much in that short statement it is practically impossible to try to start to put you right. Please go and read the two links I posted on page one.

Also this link might help you better appreciate the interconnected and inseparable nature of CoC and DoF. http://en.wikipedia.org/wiki/Hyperfocal_distance (http://en.wikipedia.org/wiki/Hyperfocal_distance)
Title: Re: How (and why) does sensor size change DOF?
Post by: Etienne on July 16, 2013, 11:08:10 AM
To be even more clear, here is an example calculation taken from http://www.cambridgeincolour.com/tutorials/digital-camera-sensor-size.htm (http://www.cambridgeincolour.com/tutorials/digital-camera-sensor-size.htm)
Title: Re: How (and why) does sensor size change DOF?
Post by: neuroanatomist on July 16, 2013, 11:12:29 AM
In practice, if you want to achieve the same depth of field on a crop as FF, you need to open the aperture on the crop camera by 1.3 stops.

In practice, it helps to give practical advice.   ::)

If I am shooting with my 85L II at f/1.2 on my 1D X, then I mount that lens on my EOS M, please tell me how, in practice, I can achieve the same DoF by opening up the aperture on the crop camera by 1.3 stops?   ::)

I understand what you mean, but it might help to phrase it the opposite way...
Title: Re: How (and why) does sensor size change DOF?
Post by: Etienne on July 16, 2013, 11:17:26 AM
In practice, if you want to achieve the same depth of field on a crop as FF, you need to open the aperture on the crop camera by 1.3 stops.

In practice, it helps to give practical advice.   ::)

If I am shooting with my 85L II at f/1.2 on my 1D X, then I mount that lens on my EOS M, please tell me how, in practice, I can achieve the same DoF by opening up the aperture on the crop camera by 1.3 stops?   ::)

I understand what you mean, but it might help to phrase it the opposite way...

Of course you can't open past max aperture. That's why some people buy FF - crop cameras can't get there (super-shallow DOF).

If you prefer: to get the deeper DOF of a crop on a FF camera you need to close the aperture by 1.3 stops on the FF camera.
Title: Re: How (and why) does sensor size change DOF?
Post by: cr316892 on July 16, 2013, 11:27:21 AM
If you take two pictures at the same position with the same lens on both a crop and a full frame, the distance between the nearest in focus object and the furthest away in focus object will be the same, so the depth of field does not change. Obviously the image captured will be different on each.

However, if you're talking about the depth of field for an equivalent picture, you'd have to move the full frame camera closer which would result in a reduced depth of field.
This is correct.

The optics are identical.

With a cropped-frame camera, you are cropping the frame. It's the equivalent of taking a picture with a full-frame camera, and cropping in Lightroom or Picasa (resolution and image quality aside).
Title: Re: How (and why) does sensor size change DOF?
Post by: privatebydesign on July 16, 2013, 04:34:31 PM
If you take two pictures at the same position with the same lens on both a crop and a full frame, the distance between the nearest in focus object and the furthest away in focus object will be the same, so the depth of field does not change. Obviously the image captured will be different on each.

However, if you're talking about the depth of field for an equivalent picture, you'd have to move the full frame camera closer which would result in a reduced depth of field.
This is correct.

The optics are identical.

With a cropped-frame camera, you are cropping the frame. It's the equivalent of taking a picture with a full-frame camera, and cropping in Lightroom or Picasa (resolution and image quality aside).

DoF does not rely solely on optics, so badgerpiper's  statement is false. DoF relies on apparent aperture (optics) and subject magnification (optics, reproduction size and viewing distance).

If you look at same sized prints, as common sense dictates you must, the crop camera capture is enlarged more, so the CoC is smaller, so the DoF is less.

Why doesn't everybody who is inclined to post read the links I have provided? It is all in there. Depending on how you make your comparison, and you have to clearly state the way you want to compare the captures, a smaller sensor can be shown to have more DoF than a ff camera, the same DoF, or as in this instance, less DoF than that ff camera.

You cannot separate DoF from subject magnification and viewing distance at the output size.

Title: Re: How (and why) does sensor size change DOF?
Post by: bdunbar79 on July 16, 2013, 06:12:53 PM
I............CAN'T................BELIEVE...............THIS............IS............SO............HARD............TO...........UNDERSTAND
Title: Re: How (and why) does sensor size change DOF?
Post by: BozillaNZ on July 16, 2013, 07:42:50 PM
DoF does not rely solely on optics, so badgerpiper's  statement is false. DoF relies on apparent aperture (optics) and subject magnification (optics, reproduction size and viewing distance).

If you look at same sized prints, as common sense dictates you must, the crop camera capture is enlarged more, so the CoC is smaller, so the DoF is less.

Why doesn't everybody who is inclined to post read the links I have provided? It is all in there. Depending on how you make your comparison, and you have to clearly state the way you want to compare the captures, a smaller sensor can be shown to have more DoF than a ff camera, the same DoF, or as in this instance, less DoF than that ff camera.

You cannot separate DoF from subject magnification and viewing distance at the output size.

Finally, someone who knows what I was talking about! I am not crazy,hahaha!

When you enlarge a picture, CoC gets bigger, DoF gets shallower. Don't believe me? Take a mild shallow DoF photo and down scale it to thumbnail image, see, suddenly everything is in focus! Magical isn't it?  :P


Note when you crop a photo, you essentially zooming in and stopping down. On the other post we had a very detailed discussion about what this does to the background blur, in short, when you zoom in and stop down, close background blurs less, distant background blurs more, and life is complicated!

http://www.canonrumors.com/forum/index.php?topic=15904.0 (http://www.canonrumors.com/forum/index.php?topic=15904.0)
Title: Re: How (and why) does sensor size change DOF?
Post by: ecka on July 17, 2013, 01:28:43 AM
DoF does not rely solely on optics, so badgerpiper's  statement is false. DoF relies on apparent aperture (optics) and subject magnification (optics, reproduction size and viewing distance).

If you look at same sized prints, as common sense dictates you must, the crop camera capture is enlarged more, so the CoC is smaller, so the DoF is less.

Why doesn't everybody who is inclined to post read the links I have provided? It is all in there. Depending on how you make your comparison, and you have to clearly state the way you want to compare the captures, a smaller sensor can be shown to have more DoF than a ff camera, the same DoF, or as in this instance, less DoF than that ff camera.

You cannot separate DoF from subject magnification and viewing distance at the output size.

Finally, someone who knows what I was talking about! I am not crazy,hahaha!

When you enlarge a picture, CoC gets bigger, DoF gets shallower. Don't believe me? Take a mild shallow DoF photo and down scale it to thumbnail image, see, suddenly everything is in focus! Magical isn't it?  :P


Note when you crop a photo, you essentially zooming in and stopping down. On the other post we had a very detailed discussion about what this does to the background blur, in short, when you zoom in and stop down, close background blurs less, distant background blurs more, and life is complicated!

http://www.canonrumors.com/forum/index.php?topic=15904.0 (http://www.canonrumors.com/forum/index.php?topic=15904.0)

That's completely insane :D.
Imagine that you have a magical shrinking machine. You print the photo say 30x20, you shrink it 100 times and it looks super sharp to you. Now you shrink yourself 100 times too and see that the picture didn't change. The problem is that your printer and monitor do not have an infinite number of pixels to show you that, and even if they did, then your eyes wouldn't see it, because they would be too small. Different print sizes that include the destructive reduction of resolution dots isn't doing any magic, you are shrinking the image, but the dots stay the same size. CoC is about the perception, not about magical information transformation. There's no such thing as magic. I say - you're both mad.
Title: Re: How (and why) does sensor size change DOF?
Post by: J.R. on July 17, 2013, 01:41:23 AM
DoF does not rely solely on optics, so badgerpiper's  statement is false. DoF relies on apparent aperture (optics) and subject magnification (optics, reproduction size and viewing distance).

If you look at same sized prints, as common sense dictates you must, the crop camera capture is enlarged more, so the CoC is smaller, so the DoF is less.

Why doesn't everybody who is inclined to post read the links I have provided? It is all in there. Depending on how you make your comparison, and you have to clearly state the way you want to compare the captures, a smaller sensor can be shown to have more DoF than a ff camera, the same DoF, or as in this instance, less DoF than that ff camera.

You cannot separate DoF from subject magnification and viewing distance at the output size.

Finally, someone who knows what I was talking about! I am not crazy,hahaha!

When you enlarge a picture, CoC gets bigger, DoF gets shallower. Don't believe me? Take a mild shallow DoF photo and down scale it to thumbnail image, see, suddenly everything is in focus! Magical isn't it?  :P


Note when you crop a photo, you essentially zooming in and stopping down. On the other post we had a very detailed discussion about what this does to the background blur, in short, when you zoom in and stop down, close background blurs less, distant background blurs more, and life is complicated!

http://www.canonrumors.com/forum/index.php?topic=15904.0 (http://www.canonrumors.com/forum/index.php?topic=15904.0)

That's completely insane :D.
Imagine that you have a magical shrinking machine. You print the photo say 30x20, you shrink it 100 times and it looks super sharp to you. Now you shrink yourself 100 times too and see that the picture didn't change. The problem is that your printer and monitor do not have an infinite number of pixels to show you that, and even if they did, then your eyes wouldn't see it, because they would be too small. Different print sizes that include the destructive reduction of resolution dots isn't doing any magic, you are shrinking the image, but the dots stay the same size. CoC is about the perception, not about magical information transformation. There's no such thing as magic. I say - you're both mad.

Title: Re: How (and why) does sensor size change DOF?
Post by: BozillaNZ on July 17, 2013, 01:45:22 AM
Prepared to shrink yourself 100 times and tell me that I am mad, LOL! I'm laughing and crying at the same time! ;D :'( ;D :'(

Even you have confirm that shrinking picture increase DoF do have a real world implication, BUT

Shrink a picture 100 times? Yes! Shrink a human 100 times? OMGWTFBBQChickenWings!

In the end, isn't photography all about perception?  ::)
Title: Re: How (and why) does sensor size change DOF?
Post by: ecka on July 17, 2013, 03:53:33 AM
Prepared to shrink yourself 100 times and tell me that I am mad, LOL! I'm laughing and crying at the same time! ;D :'( ;D :'(

Even you have confirm that shrinking picture increase DoF do have a real world implication, BUT

Shrink a picture 100 times? Yes! Shrink a human 100 times? OMGWTFBBQChickenWings!

In the end, isn't photography all about perception?  ::)

I'm glad that you are enjoying the discussion. It wasn't my intent to offend anyone.
I didn't confirm the nonsense. Shrinking the picture simply makes it's details imperceptible to you. If you can't see a bacteria, it doesn't mean that there are none. In case with a magic shrinking machine, the details are made smaller so you can still see them by shrinking yourself or maybe using a microscope. However, when you shrink the image on your screen or print a thumbnail, you are just losing the information. Just like for a half-blind person all your images can look same "sharp" or same "blurry". In fact, for him, sharp and blur looks the same. CoC is about perception. DoF is not, it is about information, same as photography. Once the light of an optical image hits the sensor, it is gone, all that's left is the information gathered by the electronics. If you shoot a picture that has nothing in focus, it doesn't matter to what resolution you downsize it, no new information will occur (except the false one). You can manipulate the image in any way you want, but in relativity to reality DoF won't change a bit. If photography is just a form of art for you and perception is the only thing that matters, then perhaps you are not even trying to understand what I'm talking about.
Title: Re: How (and why) does sensor size change DOF?
Post by: BozillaNZ on July 17, 2013, 04:23:01 AM
I'm glad that you are enjoying the discussion. It wasn't my intent to offend anyone.
I didn't confirm the nonsense. Shrinking the picture simply makes it's details imperceptible to you. If you can't see a bacteria, it doesn't mean that there are none. In case with a magic shrinking machine, the details are made smaller so you can still see them by shrinking yourself or maybe using a microscope. However, when you shrink the image on your screen or print a thumbnail, you are just losing the information. Just like for a half-blind person all your images can look same "sharp" or same "blurry". In fact, for him, sharp and blur looks the same. CoC is about perception. DoF is not, it is about information, same as photography. Once the light of an optical image hits the sensor, it is gone, all that's left is the information gathered by the electronics. If you shoot a picture that has nothing in focus, it doesn't matter to what resolution you downsize it, no new information will occur (except the false one). You can manipulate the image in any way you want, but in relativity to reality DoF won't change a bit. If photography is just a form of art for you and perception is the only thing that matters, then perhaps you are not even trying to understand what I'm talking about.

Well by your standard, in reality there is nothing really 'in focus'. The focus 'plane' is a hypothetical thing that has zero thickness. Also on the 'true' focus plane every light point has diameter of 0. Anything in front, or behind this zero thickness hypothetical plane is deemed out of focus because they have a CoC > absolute 0.

The sensor sees something in focus not because they are in focus, but simply because the CoC is smaller than sensor's pixel could distinguish. So what you say? That the image the sensor captures is the real world? It is not.

If above assumption is correct, then take an example, if I shoot a photo with a 320x240 pixel FF sensor, what is my DoF? Even my lens gives a blurry mess I would still get a 320x240 photo that is sharp at pixel level. Does this represent the 'reality'?

The thing is, reality is far weirder than you can ever imaging. We are in a photographic forum, so yes, photography is just a form of art for me and perception is the only thing that matters. I learn from my output photos and prints so I can control my equipment to get the result I want.

Then we leave the underlying physical, electricial or philosophical discussions for some one else or somewhere else.
Title: Re: How (and why) does sensor size change DOF?
Post by: ecka on July 17, 2013, 06:23:50 AM
I'm glad that you are enjoying the discussion. It wasn't my intent to offend anyone.
I didn't confirm the nonsense. Shrinking the picture simply makes it's details imperceptible to you. If you can't see a bacteria, it doesn't mean that there are none. In case with a magic shrinking machine, the details are made smaller so you can still see them by shrinking yourself or maybe using a microscope. However, when you shrink the image on your screen or print a thumbnail, you are just losing the information. Just like for a half-blind person all your images can look same "sharp" or same "blurry". In fact, for him, sharp and blur looks the same. CoC is about perception. DoF is not, it is about information, same as photography. Once the light of an optical image hits the sensor, it is gone, all that's left is the information gathered by the electronics. If you shoot a picture that has nothing in focus, it doesn't matter to what resolution you downsize it, no new information will occur (except the false one). You can manipulate the image in any way you want, but in relativity to reality DoF won't change a bit. If photography is just a form of art for you and perception is the only thing that matters, then perhaps you are not even trying to understand what I'm talking about.

Well by your standard, in reality there is nothing really 'in focus'. The focus 'plane' is a hypothetical thing that has zero thickness. Also on the 'true' focus plane every light point has diameter of 0. Anything in front, or behind this zero thickness hypothetical plane is deemed out of focus because they have a CoC > absolute 0.

The sensor sees something in focus not because they are in focus, but simply because the CoC is smaller than sensor's pixel could distinguish. So what you say? That the image the sensor captures is the real world? It is not.

If above assumption is correct, then take an example, if I shoot a photo with a 320x240 pixel FF sensor, what is my DoF? Even my lens gives a blurry mess I would still get a 320x240 photo that is sharp at pixel level. Does this represent the 'reality'?

The thing is, reality is far weirder than you can ever imaging. We are in a photographic forum, so yes, photography is just a form of art for me and perception is the only thing that matters. I learn from my output photos and prints so I can control my equipment to get the result I want.

Then we leave the underlying physical, electricial or philosophical discussions for some one else or somewhere else.


No. In reality there is nothing that is a 0. Zero is not a thing, zero is just a tool in mathematics. Every point has dimensions and it can be represented as an image of at least 1 pixel. When you are viewing ~18mp image on a ~2mp screen, then 1 dot (color) on the screen represents a group of 9 pixels of the image. Sensor does not capture the real world. The projection of an optical image on the sensor is limited by all kinds of information manipulation by the lens (diffraction, aberrations, vignetting, coma, color tint, distortion, flares and CoC). If the 9 combined pixels carry enough information to represent 1 real world dot, then it will be sharp. If not, then it will be blur (or noise). At 1:1 (100%) it is similar, but with much more false color and noise. If you shrank the blur into oblivion and got some kind of real world information, then it only means that you've destroyed all the rest and the whole blurriness carried only this little.

The sensor and electronics "sees" nothing in focus, just color and contrast of the neighboring pixels.320x240 pixel FF sensor cannot mimic human vision. There are artificial eye implants that allow blind people to see the world in just a few hundred pixels and trust me, it's nothing like the real thing. It's a blurry mess and they can only see a letter or a digit in close-up.
Title: Re: How (and why) does sensor size change DOF?
Post by: Pi on July 17, 2013, 12:08:35 PM
No. In reality there is nothing that is a 0. Zero is not a thing, zero is just a tool in mathematics.

You are wrong about DOF but I will let others argue about it. But as a mathematician, I strongly object the statement that zero is not a thing, and that there is noting at zero. How many 200-400 lenses do you own?

Quote
Every point has dimensions and it can be represented as an image of at least 1 pixel,

What if you are shooting film?
Title: Re: How (and why) does sensor size change DOF?
Post by: ecka on July 17, 2013, 01:09:20 PM
No. In reality there is nothing that is a 0. Zero is not a thing, zero is just a tool in mathematics.

You are wrong about DOF but I will let others argue about it. But as a mathematician, I strongly object the statement that zero is not a thing, and that there is noting at zero. How many 200-400 lenses do you own?

Quote
Every point has dimensions and it can be represented as an image of at least 1 pixel,

What if you are shooting film?

I don't use superteles.
Film has it's minimum dot size that can be captured.
Title: Re: How (and why) does sensor size change DOF?
Post by: dougkerr on July 17, 2013, 01:42:00 PM
First recall that DoF is not a distance that comes solely from optical theory (like the distance to the image for a certain object location); it is a description of the range of object distances over which a certain arbitrarily-adopted criterion of "blurred-ness" is not exceeded, with the camera focused at a certain distance.

Often, for consistency, that criterion is a blur circle whose diameter is a certain fraction of the overall image size (maybe its diagonal size). This relates to a consistent diameter blur circle on an image produced at a consistent size (such as a consistent size print).

That having been said, when we compare the DoF attained for two values of some attribute of the camera (such as sensor size), "all other factors being equal", we must adopt and announce what we mean by  "all other factors being equal".

Here is one set of such that we might adopt:

a.  Focal length such that the field of view is the same in both setups.  (Aha!)

b. Camera focused at the same distance.  (Of course.)

c. Same f-number.  (Of course.)

d. Criterion for "acceptable" blurring the same in terms of blur circle diameter as a fraction of the image size (diagonal will do).

Now, if we are comparing two cameras, with "B" having an image size 2x that of "A":

1.  Under rule a, we must use a lens of twice the focal length in B as in A.

2. Under rule c, our acceptable diameter of blur circle is twice for B as it is for A.

Now, with regard to point 2, that means that we are more tolerant of blur in B than in A. Thus this consideration alone would lead to a greater depth of field for B than A.

This works essentially proportionally to the blur circle diameter criterion, and thus to image size (sensor size).

Remember, depth of field is not an creature of optical theory alone. It is a creature of what amount of blurring we consider "acceptable". If we increase the amount we consider "acceptable", then our focus distance can be more "off" and we still consider the result acceptable.

Now, to point 1. Because of the optical situation involved (and I will not attempt to describe this in detail here), for a greater focal length the "incorrectness" in focus distance to cause a certain diameter blur circle is less. Thus this consideration alone would lead to a lesser depth of field for B than A.

This works essentially proportionally to the square of the focal length, and thus (because of rule a) to the square of the image size (sensor size).

So as we move from A to B, we find that issue 2 gives an increase in the depth of field, and issue 1 gives a larger decrease in the depth of field (because it varies inversely as the square of the image size).

Thus, the overall effect is that (under the rules stated above), for an increase in sensor size we have a net decrease in depth of field.

Quod erat demonstrandum.

Best regards,

Doug
Title: Re: How (and why) does sensor size change DOF?
Post by: bdunbar79 on July 17, 2013, 02:33:26 PM
Speaking about sensor size changing the DOF is a bit misleading. Do we keep everything else the same? This is actually impossible. You cannot keep the AOV and the FL the same. If we just swap the bodies, without changing (physically) anything else, smaller sensors have less DOF.

For the same AOV and same f/stop, larger sensors with the corresponding lenses have less DOF because the "physical aperture" is larger. For example, 80/2>50/2. There is no rule saying you must shoot at the same f-stops with both sensors, and if you shoot with equivalents ones (like 80/3.2 vs. 50/2) DOF is the same. That means "faster" lenses for the smaller sensor. They do not always exists, but sometimes, they do. For example, the m43 system has f/2 zooms, eq. to f/4 ones. They also have a f/0.95 prime, eq. to an f/2 one. But they do not have a match for f/1.4 on FF.

Bottom line: it is not the sensor size, it is the lens and the sensor but lenses with less DOF for larger sensors are easier to make, more common, cost less, and resolve more.

Yes you are correct obviously.  But what I was getting at, is if you shoot with a 1Dx with a 50mm lens at f/4, and then you change to a 7D, and don't move:  Obviously the DOF is not the same.  Move back to the same AoV and the DOF is STILL not the same.  Now you have to change aperture.  So those that are saying sensor size has nothing to do with it, well...

Look at the things I had to change, simply because of a different sensor size.  I guess I don't get why this has gone so far.  That is all I am trying to say.
Title: Re: How (and why) does sensor size change DOF?
Post by: Meh on July 17, 2013, 04:38:19 PM
Shrinking the picture simply makes it's details imperceptible to you.

If I may, can I suggest that this one sentence sums up some of the disagreement in this thread.   DoF is, in fact, a concept that is rooted in human visual perception.  DoF is defined as the distance in front of and behind the plane of focus that appears in focus to a human being.  The calculation requires assumptions regarding human visual acuity, print size, and viewing distance.

I believe, others can correct me if I'm wrong, it is also implicitly assumed that the print size and resolution is such that the individual pixels in the print are too small for the viewer to see them at the assumed print size and viewing distance.  If the pixels are visible then the entire image would not appear sharp.  That is why sensor resolution does not appear in the calculation.

So yes,  print size matters and yes, if you print small enough the entire image would "magically" appear sharp.  "Appear" is the operative word in that statement but it is relevant because "appears sharp" is fundamental to the concept of DoF.  If you also shrunk yourself down, your visual acuity would likely also change so in fact DoF would be the same.

And it is a concept.  It is a defined value based on some reasonable assumptions.  DoF is not something that exists independent of human vision and is not a strictly defined measurement like mass, distance, size, etc.

If you're looking for a physically defined parameter, it exists.  That is focus distance.  The distance from the image plane that is precisely in focus (in practical terms it would be maximally in focus because there is no perfect focus).  And there is only one distance that is maximally in focus... every plane in front of and behind the focus plane is less focused.  If human visual acuity was infinite and the resolution of a print was infinite you would be able to see the tiniest difference in sharpness.  But that's not the case, more than just the exact plane of focus appears sharp and we can define the depth in the image that appears sharp... i.e. Depth of Field.
Title: Re: How (and why) does sensor size change DOF?
Post by: Marsu42 on July 17, 2013, 09:16:42 PM
DoF does not rely solely on optics, so badgerpiper's  statement is false. DoF relies on apparent aperture (optics) and subject magnification (optics, reproduction size and viewing distance).

Thank you very much that you are so persistent explaining it, simple /me really learned a lot in this thread from you and the links you posted, esp. http://www.josephjamesphotography.com/equivalence/light.htm#dof

I was mislead by the dof calculators that output a precise dof range, I never read the fine print :-> ... but on the other hand I knew that the apparent dof changes drastically with perceived image size (like from camera display -> large lcd and your distance from it) which actually requires you to take multiple shots of the same scene with different apertures to have the dof *you* want for every output situation you have in mind. The CoC explains this and having read about it I don't know how I could have ever thought dof would only depend on optics :-p
Title: Re: How (and why) does sensor size change DOF?
Post by: privatebydesign on July 17, 2013, 10:07:44 PM
DoF does not rely solely on optics, so badgerpiper's  statement is false. DoF relies on apparent aperture (optics) and subject magnification (optics, reproduction size and viewing distance).

Thank you very much that you are so persistent explaining it, simple /me really learned a lot in this thread from you and the links you posted, esp. http://www.josephjamesphotography.com/equivalence/light.htm#dof

I was mislead by the dof calculators that output a precise dof range, I never read the fine print :-> ... but on the other hand I knew that the apparent dof changes drastically with perceived image size (like from camera display -> large lcd and your distance from it) which actually requires you to take multiple shots of the same scene with different apertures to have the dof *you* want for every output situation you have in mind. The CoC explains this and having read about it I don't know how I could have ever thought dof would only depend on optics :-p

You are so so welcome.

For another mind numbing factoid related to dof, we all think DSLR's are WYSIWYG when shooting wide open, however look through a fast lens (>f2) mounted on your camera, then take a picture and compare the dof of the image to the scene through your camera. The image will have much narrower dof, focusing screens have an aperture! It is around f2.8 so when you shoot wider than that you get much shallower dof than you expect. As a follow on to this it is impossible to accurately manually focus an ultra fast lens with our standard focusing screens.
Title: Re: How (and why) does sensor size change DOF?
Post by: neuroanatomist on July 17, 2013, 11:04:18 PM
DoF does not rely solely on optics, so badgerpiper's  statement is false. DoF relies on apparent aperture (optics) and subject magnification (optics, reproduction size and viewing distance).

Thank you very much that you are so persistent explaining it, simple /me really learned a lot in this thread from you and the links you posted, esp. http://www.josephjamesphotography.com/equivalence/light.htm#dof

I was mislead by the dof calculators that output a precise dof range, I never read the fine print :-> ... but on the other hand I knew that the apparent dof changes drastically with perceived image size (like from camera display -> large lcd and your distance from it) which actually requires you to take multiple shots of the same scene with different apertures to have the dof *you* want for every output situation you have in mind. The CoC explains this and having read about it I don't know how I could have ever thought dof would only depend on optics :-p

You are so so welcome.

For another mind numbing factoid related to dof, we all think DSLR's are WYSIWYG when shooting wide open, however look through a fast lens (>f2) mounted on your camera, then take a picture and compare the dof of the image to the scene through your camera. The image will have much narrower dof, focusing screens have an aperture! It is around f2.8 so when you shoot wider than that you get much shallower dof than you expect. As a follow on to this it is impossible to accurately manually focus an ultra fast lens with our standard focusing screens.

Yep - the stock screens are laser microetched to make them brighter with slow lenses, and that's the consequence.  Not only are you getting the DoF of ~f/2.8 through the VF, you're getting that brightness even with a faster lens.  You can see the effect of this with bodies with a transmissive LCD (7D, 5DIII, 1D X) - with a fast lens (f/1.2-1.4), the AF point display is a sort of washed out gray, not black.  As you stop down with the DoF preview button pressed, the VF doesn't get dimmer, but the transmissive LCD gets progressively darker until ~f/2.5, then the whole VF starts getting darker, too.
Title: Re: How (and why) does sensor size change DOF?
Post by: ecka on July 18, 2013, 04:47:27 AM
Shrinking the picture simply makes it's details imperceptible to you.

If I may, can I suggest that this one sentence sums up some of the disagreement in this thread.   DoF is, in fact, a concept that is rooted in human visual perception.  DoF is defined as the distance in front of and behind the plane of focus that appears in focus to a human being.  The calculation requires assumptions regarding human visual acuity, print size, and viewing distance.

I believe, others can correct me if I'm wrong, it is also implicitly assumed that the print size and resolution is such that the individual pixels in the print are too small for the viewer to see them at the assumed print size and viewing distance.  If the pixels are visible then the entire image would not appear sharp.  That is why sensor resolution does not appear in the calculation.

So yes,  print size matters and yes, if you print small enough the entire image would "magically" appear sharp.  "Appear" is the operative word in that statement but it is relevant because "appears sharp" is fundamental to the concept of DoF.  If you also shrunk yourself down, your visual acuity would likely also change so in fact DoF would be the same.

And it is a concept.  It is a defined value based on some reasonable assumptions.  DoF is not something that exists independent of human vision and is not a strictly defined measurement like mass, distance, size, etc.

If you're looking for a physically defined parameter, it exists.  That is focus distance.  The distance from the image plane that is precisely in focus (in practical terms it would be maximally in focus because there is no perfect focus).  And there is only one distance that is maximally in focus... every plane in front of and behind the focus plane is less focused.  If human visual acuity was infinite and the resolution of a print was infinite you would be able to see the tiniest difference in sharpness.  But that's not the case, more than just the exact plane of focus appears sharp and we can define the depth in the image that appears sharp... i.e. Depth of Field.

I don't know. I disagree, that when I photograph a ruler which clearly shows that the DoF is, let's say, ~15mm, I must let the shrink size decide that the DoF is actually half a meter or that I was shooting at hyperfocal and I'm crazy :).
I thought that DoF is the thickness of the sharp focus plane your camera can capture (how is it called then?). Turns out I was wrong, it is what anyone wants it to be and if it can't be, then just get a better printer :D.
I say, if you have to shrink your images to make everything look sharp, then you are using the wrong camera format.
DoF area is sharp, but sharpness ≠ DoF
Title: Re: How (and why) does sensor size change DOF?
Post by: BozillaNZ on July 18, 2013, 05:53:15 AM
It seems there's nothing constructive I can add to this post now. Everyone except one agrees on the common knowledge about relationship between output magnification and DoF. The post starter can either agree we us, or him or come up with his own conclusion.
Title: Re: How (and why) does sensor size change DOF?
Post by: Matthew19 on July 18, 2013, 06:04:56 AM
The simplest answer is from Gale Tattersall, DP of the TV show HOUSE : a larger sensor requires a longer lens to achieve the same field of view. The longer the lens the less DOF. (aperture staying the same of course)
Title: Re: How (and why) does sensor size change DOF?
Post by: Marsu42 on July 18, 2013, 07:06:05 AM
It is around f2.8 so when you shoot wider than that you get much shallower dof than you expect. As a follow on to this it is impossible to accurately manually focus an ultra fast lens with our standard focusing screens.

For once, I knew this, but I've got a question since you or neuro probably have tried these screens: Amazon customer reviews tell me that the effect of the more visible dof is not that large, while the effect of a darker vf for slower lenses is significant - bottom line to only get this screen if you shoot f1.2-f1.4 wide open very often, correct?

As you stop down with the DoF preview button pressed, the VF doesn't get dimmer, but the transmissive LCD gets progressively darker until ~f/2.5, then the whole VF starts getting darker, too.

... meaning the exchangeable screen for lesser cameras also has zero effect for f2.8 lenses, but only for f2.5 or faster? I was never able to research how large the effect of the screen is for what aperture, and unfortunately you cannot try these in a shop.

Title: Re: How (and why) does sensor size change DOF?
Post by: Sporgon on July 18, 2013, 07:32:08 AM

... meaning the exchangeable screen for lesser cameras also has zero effect for f2.8 lenses, but only for f2.5 or faster? I was never able to research how large the effect of the screen is for what aperture, and unfortunately you cannot try these in a shop.


At 2.8 there is a slight benefit in real DoF, maybe just due to more definition between in and out of focus. However the viewfinder is slightly darker even at 2.8. Although they are called  'manual focus' screens I've found them to be beneficial only with very fast primes: f1.2 - 2, so they are more of a 'fast prime' screen really.
Title: Re: How (and why) does sensor size change DOF?
Post by: Sporgon on July 18, 2013, 07:55:43 AM
Quote from: bdunbar79 link=topic=15884.msg292208#

Yes you are correct obviously.  But what I was getting at, is if you shoot with a 1Dx with a 50mm lens at f/4, and then you change to a 7D, and don't move:  Obviously the DOF is not the same.  Move back to the same AoV and the DOF is STILL not the same.  Now you have to change aperture.  So those that are saying sensor size has nothing to do with it, well...




There's a practical photographer speaking.

In practical use of course sensor size effects DoF. OK, it's influence is indirect because of the lens focal length and distance you're going to use, but as you cannot produce a picture without both lens and sensor, the sensor size does, indirectly, effect DoF.

Title: Re: How (and why) does sensor size change DOF?
Post by: neuroanatomist on July 18, 2013, 08:31:05 AM
... meaning the exchangeable screen for lesser cameras also has zero effect for f2.8 lenses, but only for f2.5 or faster? I was never able to research how large the effect of the screen is for what aperture, and unfortunately you cannot try these in a shop.
At 2.8 there is a slight benefit in real DoF, maybe just due to more definition between in and out of focus. However the viewfinder is slightly darker even at 2.8. Although they are called  'manual focus' screens I've found them to be beneficial only with very fast primes: f1.2 - 2, so they are more of a 'fast prime' screen really.

Chuck Westfall has stated, 'faster than f/4'.  Personally, I don't see a lot of difference at f/2.8, but there is some.  It's not really enough to change how I'd compose a shot, but at f/1.2 or f/1.8, the difference is very noticeable. 
Title: Re: How (and why) does sensor size change DOF?
Post by: Pi on July 18, 2013, 01:33:19 PM
The simplest answer is from Gale Tattersall, DP of the TV show HOUSE : a larger sensor requires a longer lens to achieve the same field of view. The longer the lens the less DOF. (aperture staying the same of course)

Which aperture: the f-stop or the physical one?

If it is the former, start with the 200/2 on crop. How do you get less (EDIT) DOF with 320mm on FF?
Title: Re: How (and why) does sensor size change DOF?
Post by: privatebydesign on July 18, 2013, 01:52:42 PM
The simplest answer is from Gale Tattersall, DP of the TV show HOUSE : a larger sensor requires a longer lens to achieve the same field of view. The longer the lens the less DOF. (aperture staying the same of course)

Which aperture: the f-stop or the physical one?

If it is the former, start with the 200/2 on crop. How do you get more DOF with 320mm on FF?

Mr Tattersall was over simplifying.

How do you get more DOF with a FF than a 200/f2 on a crop camera. Easy, use a lens with a smaller physical aperture than 100mm, a 100-400 f4-5.6 would do the job.

If you wanted equivalency, i.e close to identical images from both cameras from the same spot you'd need to do this


Obviously a 300 f2.8 on a ff camera outperforms a 200 f2 on a crop camera with regards thin dof, it also makes smoother and much more blurred backgrounds. People who espouse the 200 f2 as having a "unique look", are missing the point, a 300 f2.8 demonstrates all the "unique" qualities of the 200 f2, isolation, big background blur, narrow dof, only it does them all "better".
Title: Re: How (and why) does sensor size change DOF?
Post by: Pi on July 18, 2013, 04:27:28 PM
The simplest answer is from Gale Tattersall, DP of the TV show HOUSE : a larger sensor requires a longer lens to achieve the same field of view. The longer the lens the less DOF. (aperture staying the same of course)

Which aperture: the f-stop or the physical one?

If it is the former, start with the 200/2 on crop. How do you get more DOF with 320mm on FF?

Mr Tattersall was over simplifying.

How do you get more DOF with a FF than a 200/f2 on a crop camera. Easy, use a lens with a smaller physical aperture than 100mm, a 100-400 f4-5.6 would do the job.

I meant: how do you get less DOF, which was consistent with the post I replied to. And, to be more precise, how do you get 1 1/3 stop less, which is what the difference in the sensor sizes suggests.
Title: Re: How (and why) does sensor size change DOF?
Post by: privatebydesign on July 18, 2013, 04:39:49 PM
The simplest answer is from Gale Tattersall, DP of the TV show HOUSE : a larger sensor requires a longer lens to achieve the same field of view. The longer the lens the less DOF. (aperture staying the same of course)

Which aperture: the f-stop or the physical one?

If it is the former, start with the 200/2 on crop. How do you get more DOF with 320mm on FF?

Mr Tattersall was over simplifying.

How do you get more DOF with a FF than a 200/f2 on a crop camera. Easy, use a lens with a smaller physical aperture than 100mm, a 100-400 f4-5.6 would do the job.

I meant: how do you get less DOF, which was consistent with the post I replied to. And, to be more precise, how do you get 1 1/3 stop less, which is what the difference in the sensor sizes suggests.

Shoot with a 300 f2.8 on your ff @ f2.8. That is how.
Title: Re: How (and why) does sensor size change DOF?
Post by: Pi on July 18, 2013, 04:53:08 PM
Shoot with a 300 f2.8 on your ff @ f2.8. That is how.

And I get 1 1/3 stop less DOF? Really? You calculator shows the same DOF (in fact it is a bit less with FF but far from 1 1/3 stop).

What if I shoot with the 200/1.8 on crop?
Title: Re: How (and why) does sensor size change DOF?
Post by: privatebydesign on July 18, 2013, 05:27:19 PM
Shoot with a 300 f2.8 on your ff @ f2.8. That is how.

And I get 1 1/3 stop less DOF? Really? You calculator shows the same DOF (in fact it is a bit less with FF but far from 1 1/3 stop).

What if I shoot with the 200/1.8 on crop?

I don't understand what you are getting at. You will always be able to do things with one format you can't do with another, that is why one is not "better" than the other for everybody. The simplest workaround for your contrived example is to buy a 1.4 TC for the ff camera, that gets you within 1/3 stop of equivalence values.

However, let me flip your scenario, tell me how to take a one shot crop camera equivalent of a ff that is using a 17 TS-E? Or a 15mm fisheye f2.8? Or a 200 f2/1.8? Or a 50mm f1.2? Or an 85mm f1.2? Tell me how you could do 1:1 images of anything over 22mm with a crop camera, the list goes on and on. For some people most of these will never be important, for others just one makes a particular sensor size over another worthwhile

I recently advised a pro photographer on an equipment purchase. His ideal camera for his intended output, low resolution web based event work, was a 4/3 sensor. That gave him deeper dof and more than adequate output quality.
Title: Re: How (and why) does sensor size change DOF?
Post by: Sporgon on July 18, 2013, 05:53:55 PM
Quote from: privatebydesign link=topic=15884.msg292626#msg292626 date=

Obviously a 300 f2.8 on a ff camera outperforms a 200 f2 on a crop camera with regards thin dof, it also makes smoother and much more blurred backgrounds. People who espouse the 200 f2 as having a "unique look", are missing the point, a 300 f2.8 demonstrates all the "unique" qualities of the 200 f2, isolation, big background blur, narrow dof, only it does them all "better".


I presume the same thing applies to the 135 f2 and 200 f2.8. Personally I've always found the latter to be the better all round lens
Title: Re: How (and why) does sensor size change DOF?
Post by: Wild on July 18, 2013, 06:35:05 PM
Also here, http://www.josephjamesphotography.com/equivalence/ (http://www.josephjamesphotography.com/equivalence/) for a very detailed insight into sensor sizes and their interaction with focal length, dof, aperture and iso. Yes, even iso has a crop factor!
Privatebydesign, thanks for the great link. Lots of fun explanations in there. However, I'm still not sure how print size and viewing distance affect DOF. Is there another explanation somewhere, or maybe some examples?

Btw, I've tried just resizing some of my photos on my monitor and seeing if they seem to have more/less DOF and can't really tell a difference...maybe I'm doing it wrong.
Title: Re: How (and why) does sensor size change DOF?
Post by: Pi on July 18, 2013, 07:02:43 PM
Shoot with a 300 f2.8 on your ff @ f2.8. That is how.

And I get 1 1/3 stop less DOF? Really? You calculator shows the same DOF (in fact it is a bit less with FF but far from 1 1/3 stop).

What if I shoot with the 200/1.8 on crop?

I don't understand what you are getting at.

Going back to my post yesterday - in reply to Mathew, I think. You cannot just say - keep the aperture (the f-stop, to be more precise) the same with FF, and you get less DOF. Sometimes you just cannot keep the f-stop the same because there is no, say, 320/2 lens or similar. Most of the time, larger sensor does allow for less DOF with the same AOV but this depends on what lenses you have available, and what lenses you could possibly have available.

When you go to telephoto lenses, the limiting factor is often the physical aperture, not the f-stop. You just cannot increase the FL and keep the f-stop the same in many cases. I did not say anything about other scenarios.

Quote
I recently advised a pro photographer on an equipment purchase. His ideal camera for his intended output, low resolution web based event work, was a 4/3 sensor. That gave him deeper dof and more than adequate output quality.

That might have been a good advice with one exception - the m43 does not provide deeper DOF! You can get as much DOF as you want with any sensor size if you stop well enough until diffraction starts making everything so blurry that talking about DOF becomes meaningless.
Title: Re: How (and why) does sensor size change DOF?
Post by: privatebydesign on July 18, 2013, 07:14:28 PM
Also here, http://www.josephjamesphotography.com/equivalence/ (http://www.josephjamesphotography.com/equivalence/) for a very detailed insight into sensor sizes and their interaction with focal length, dof, aperture and iso. Yes, even iso has a crop factor!
Privatebydesign, thanks for the great link. Lots of fun explanations in there. However, I'm still not sure how print size and viewing distance affect DOF. Is there another explanation somewhere, or maybe some examples?

Btw, I've tried just resizing some of my photos on my monitor and seeing if they seem to have more/less DOF and can't really tell a difference...maybe I'm doing it wrong.

Here is an example. I took this image for an artists show, it was printed to 46"x31". As a 700px web image most would agree the zip picture left, by her right cheek, is within acceptable focus, at f7.1 with a 100mm lens it is well within a dof calculators range. The second image is what that zip looks like when I printed it at 46" and viewed from the same distance. Clearly it is not now in acceptable focus. The only thing that has changed is the subject magnification. We have increased the CoC to such an extent that it no longer holds true, we can clearly differentiate between a point and a circle. To bring it back into acceptable focus we all we need to do is increase our viewing distance, step back from your monitor, across a room, and the zip will become sharp again.

Cool isn't it?  :)
Title: Re: How (and why) does sensor size change DOF?
Post by: privatebydesign on July 19, 2013, 12:33:25 AM
Pi,

I still don't understand what you are getting at, other than making a point that some lenses don't exist, but that is so obvious I didn't think it needed saying.

For equivalency purposes there are many more situations where a crop camera can't replicate a single shot from a ff camera than the other way around. A ff and 300 f2.8 might not give appreciably less dof than a 200 f2 on a crop camera, but what if you want less dof with the crop camera too? Of course you could always use a Nikon 300 f2 and an adapter to get less dof with the ff camera. However, my point was you can take essentially the same image with both formats with available lenses in your scenario, you can't in any of the multitude I laid out.

As for the 4/3 providing more dof, it depends how you look at it. Take a scenario where output is modest print and web sized, so iso and noise is not a concern, you have a set EV/exposure, of say 1/60 sec, f5.6, iso 400. Now if I shoot a ff capture at 10 feet with those settings and a 50mm lens I'd have a total of 4.25 ft dof, not bad but not very practical for event shooting and group shots. However, on my 4/3 camera I'd get the same fov with a 25mm lens, if I used the same settings for my exposure, 1/60 sec, f5.6, iso 400 I'd get a dof that included everything from 7 feet to 17 feet, a far better range for group shots.

Now you could argue that I could replicate my 4/3 shot with the ff camera at f11 and iso 1600, and you'd be correct, but the 4/3 is going to cost much less, be much smaller and lighter etc etc. That is why it was sound advice for him to get a 4/3 camera.
Title: Re: How (and why) does sensor size change DOF?
Post by: ecka on July 19, 2013, 02:50:30 AM
Also here, http://www.josephjamesphotography.com/equivalence/ (http://www.josephjamesphotography.com/equivalence/) for a very detailed insight into sensor sizes and their interaction with focal length, dof, aperture and iso. Yes, even iso has a crop factor!
Privatebydesign, thanks for the great link. Lots of fun explanations in there. However, I'm still not sure how print size and viewing distance affect DOF. Is there another explanation somewhere, or maybe some examples?

Btw, I've tried just resizing some of my photos on my monitor and seeing if they seem to have more/less DOF and can't really tell a difference...maybe I'm doing it wrong.

Here is an example. I took this image for an artists show, it was printed to 46"x31". As a 700px web image most would agree the zip picture left, by her right cheek, is within acceptable focus, at f7.1 with a 100mm lens it is well within a dof calculators range. The second image is what that zip looks like when I printed it at 46" and viewed from the same distance. Clearly it is not now in acceptable focus. The only thing that has changed is the subject magnification. We have increased the CoC to such an extent that it no longer holds true, we can clearly differentiate between a point and a circle. To bring it back into acceptable focus we all we need to do is increase our viewing distance, step back from your monitor, across a room, and the zip will become sharp again.

Cool isn't it?  :)

This is only an illusion of sharpness. The truth is what really matters (the information). Looking at the print from far away only proves that human vision is very limited. At close-up you can see all the information captured by your camera, both sharp and blurry parts. So, sharpness = information. Then from the distance you see much much less information despite that it looks sharper. This kind of sharpness ≠ information. This trick is about the CoC of your eyes, DoF has nothing to do with it.
Title: Re: How (and why) does sensor size change DOF?
Post by: Pi on July 19, 2013, 03:10:50 AM
Now you could argue that I could replicate my 4/3 shot with the ff camera at f11 and iso 1600,

Consider that I said it.  :)

Quote
and you'd be correct, but the 4/3 is going to cost much less, be much smaller and lighter etc etc. That is why it was sound advice for him to get a 4/3 camera.

I did say that it was probably a good advice. But the fact remains: smaller formats do not allow you to get deeper DOF.
Title: Re: How (and why) does sensor size change DOF?
Post by: Wild on July 19, 2013, 04:17:22 AM
Here is an example. I took this image for an artists show, it was printed to 46"x31". As a 700px web image most would agree the zip picture left, by her right cheek, is within acceptable focus, at f7.1 with a 100mm lens it is well within a dof calculators range. The second image is what that zip looks like when I printed it at 46" and viewed from the same distance. Clearly it is not now in acceptable focus. The only thing that has changed is the subject magnification. We have increased the CoC to such an extent that it no longer holds true, we can clearly differentiate between a point and a circle. To bring it back into acceptable focus we all we need to do is increase our viewing distance, step back from your monitor, across a room, and the zip will become sharp again.

Cool isn't it?  :)

Thanks for the example! Now that I've seen the example, I definitely understand where you're coming from.

Practically speaking, I know you're right about the depth of field being dependent upon print size, but from a mathematical perspective, isn't depth of field still the same?

In other words, if we were to define a specific "sharpness" level as a minimum threshold for being considered in focus, wouldn't the two images, no matter what size, have the same areas of the image being "in focus?" Without the limitations of our vision, technically the images have the same depth of field, even if we can't discern the difference, right? Please correct me if I'm way off here.
Title: Re: How (and why) does sensor size change DOF?
Post by: neuroanatomist on July 19, 2013, 07:41:12 AM
This is only an illusion of sharpness. The truth is what really matters (the information). Looking at the print from far away only proves that human vision is very limited. At close-up you can see all the information captured by your camera, both sharp and blurry parts. So, sharpness = information. Then from the distance you see much much less information despite that it looks sharper. This kind of sharpness ≠ information. This trick is about the CoC of your eyes, DoF has nothing to do with it.

Sorry, but DoF has everything to do with it. I suggest you acquaint yourself with the definition of depth of field, and note that part of that definition includes output size and viewing distance.  There is no such thing as an 'objective' DoF.  Assumptions can be made, and must be made (although they're not always stated) for DoF calculators, etc. - those include an arbitrarily chosen output size and viewing distance, without which a determination of DoF is meaningless.
Title: Re: How (and why) does sensor size change DOF?
Post by: privatebydesign on July 19, 2013, 08:25:54 AM
Also here, http://www.josephjamesphotography.com/equivalence/ (http://www.josephjamesphotography.com/equivalence/) for a very detailed insight into sensor sizes and their interaction with focal length, dof, aperture and iso. Yes, even iso has a crop factor!
Privatebydesign, thanks for the great link. Lots of fun explanations in there. However, I'm still not sure how print size and viewing distance affect DOF. Is there another explanation somewhere, or maybe some examples?

Btw, I've tried just resizing some of my photos on my monitor and seeing if they seem to have more/less DOF and can't really tell a difference...maybe I'm doing it wrong.

Here is an example. I took this image for an artists show, it was printed to 46"x31". As a 700px web image most would agree the zip picture left, by her right cheek, is within acceptable focus, at f7.1 with a 100mm lens it is well within a dof calculators range. The second image is what that zip looks like when I printed it at 46" and viewed from the same distance. Clearly it is not now in acceptable focus. The only thing that has changed is the subject magnification. We have increased the CoC to such an extent that it no longer holds true, we can clearly differentiate between a point and a circle. To bring it back into acceptable focus we all we need to do is increase our viewing distance, step back from your monitor, across a room, and the zip will become sharp again.

Cool isn't it?  :)

This is only an illusion of sharpness. The truth is what really matters (the information). Looking at the print from far away only proves that human vision is very limited. At close-up you can see all the information captured by your camera, both sharp and blurry parts. So, sharpness = information. Then from the distance you see much much less information despite that it looks sharper. This kind of sharpness ≠ information. This trick is about the CoC of your eyes, DoF has nothing to do with it.

DoF is only an illusion of sharpness.
Title: Re: How (and why) does sensor size change DOF?
Post by: privatebydesign on July 19, 2013, 08:39:52 AM
Now you could argue that I could replicate my 4/3 shot with the ff camera at f11 and iso 1600,

Consider that I said it.  :)

Quote
and you'd be correct, but the 4/3 is going to cost much less, be much smaller and lighter etc etc. That is why it was sound advice for him to get a 4/3 camera.

I did say that it was probably a good advice. But the fact remains: smaller formats do not allow you to get deeper DOF.

As I wrote in my first post in this thread, the second post on page one, depending on how you make your comparison a crop sensor can be shown to demonstrate more, the same, or even less dof than a ff sensor.

The truth is, two photographers standing next to each other, one crop sensor, the other ff sensor, with exactly the same camera settings and the same framed image (meaning the crop owner has a wider lens), if they both take an image then the crop sensor image has more dof. You can argue the semantics and explain it is the lens that is making the difference, and that is fine (we have done a lot of that in this thread), but in practical terms to many actual photographers the difference is most readily associated with sensor size.

Or, 'If I take this framed image from a set point with these settings how much dof do I get with this sensor/lens combination?' that is a question many photographers would ask and the smaller sensor/wider lens combo will realise more dof.

Technically a smaller sensor displays narrower dof, after all for a standardised output the CoC must be smaller as it needs more enlargement, however, for same framed images the difference in focal length and apparent aperture far over power the CoC differences.

Or, consider the corollary of your statement "But the fact remains: smaller formats do not allow you to get deeper DOF.", that would be, larger formats do not allow you to shoot narrower dof. Show me a narrow dof image from a P&S, or a phone, you are just arguing semantic points, not embracing the way we actually understand and use the equipment available to us. Sure if somebody made a sub f1 P&S we "could" take a narrow dof image, but they don't. Similarly you can't shoot an image that replicates a 200 f2 on a ff body with a single shot from a crop camera (but you can the other way around).
Title: Re: How (and why) does sensor size change DOF?
Post by: ecka on July 19, 2013, 09:00:51 AM
... I thought that DoF is the thickness of the sharp focus plane your camera can capture (how is it called then?)...
... the thickness in reality, not in the picture.

...There is no such thing as an 'objective' DoF...

Do we need a new definition here? Because I'm pretty sure that OP was asking about THAT THING, not the CoC.
Title: Re: How (and why) does sensor size change DOF?
Post by: privatebydesign on July 19, 2013, 09:19:08 AM

Thanks for the example! Now that I've seen the example, I definitely understand where you're coming from.

Practically speaking, I know you're right about the depth of field being dependent upon print size, but from a mathematical perspective, isn't depth of field still the same?

In other words, if we were to define a specific "sharpness" level as a minimum threshold for being considered in focus, wouldn't the two images, no matter what size, have the same areas of the image being "in focus?" Without the limitations of our vision, technically the images have the same depth of field, even if we can't discern the difference, right? Please correct me if I'm way off here.

Yes, the same area, as a percentage of the total image area. That is where your enlargement and viewing distance come in. Enlarge a point and it gets bigger and more obvious until it is a circle, but it stays the same size in relation to the image as a whole. CoC is just about setting a standard about the distance at which a sharp point becomes a blurred circle to a humans eye, you cannot take the human eye out of the equation because the very definition of DoF contains the words "acceptably sharp" or "beyond the resolution of the human eye". That is a subjective element that is generalised to 0.2mm at 25cm in the final output. Obviously if we stand back our eyesight becomes the limiting factor so we can increase the CoC.

Maintain a reproduction size and viewing distance ratio such that the CoC (point at which you can't see the difference between a point and a circle) and you can go as big, or as small, as you'd like.
Title: Re: How (and why) does sensor size change DOF?
Post by: privatebydesign on July 19, 2013, 09:27:09 AM
... I thought that DoF is the thickness of the sharp focus plane your camera can capture (how is it called then?)...
... the thickness in reality, not in the picture.

...There is no such thing as an 'objective' DoF...

Do we need a new definition here? Because I'm pretty sure that OP was asking about THAT THING, not the CoC.

The plane of focus has no depth. Imagine it as a sheet of the thinnest paper, only much thinner. Everything in front of, and behind, that sheet of paper is less sharp than whatever is on the sheet of paper. Because of limitations to our eyesight something very close to the paper might look in focus, but it isn't, at some point as you move towards the paper things become more obviously out of focus, you have now surpassed your DoF/CoC criteria, but, step back and you again can't see the differences because your eyesight can't resolve it.
Title: Re: How (and why) does sensor size change DOF?
Post by: ecka on July 19, 2013, 09:56:07 AM
... I thought that DoF is the thickness of the sharp focus plane your camera can capture (how is it called then?)...
... the thickness in reality, not in the picture.

...There is no such thing as an 'objective' DoF...

Do we need a new definition here? Because I'm pretty sure that OP was asking about THAT THING, not the CoC.

The plane of focus has no depth. Imagine it as a sheet of the thinnest paper, only much thinner. Everything in front of, and behind, that sheet of paper is less sharp than whatever is on the sheet of paper. Because of limitations to our eyesight something very close to the paper might look in focus, but it isn't, at some point as you move towards the paper things become more obviously out of focus, you have now surpassed your DoF/CoC criteria, but, step back and you again can't see the differences because your eyesight can't resolve it.

I agree that the focus plane of an optical image projection is thinner than it looks like. That's what the CoC thing is all about. However, the sensor resolution is limited and it has it's smallest possible dot size which is a pixel and which is a constant for a given camera.

Maintain a reproduction size and viewing distance ratio such that the CoC (point at which you can't see the difference between a point and a circle) and you can go as big, or as small, as you'd like.

No, you cannot do that. It could only apply to a camera with an infinite number of pixels. If a pixel is too big, then it becomes a square. If it's too small, then it disappears.
In all my statements I assumed that both FF and APSC sensors had the same pixel pitch. Otherwise, even the same format cameras (same sensor size) with different megapixel numbers (like 12 vs 36) should have different DoF/CoC characteristics.
Title: Re: How (and why) does sensor size change DOF?
Post by: privatebydesign on July 19, 2013, 10:09:32 AM
... I thought that DoF is the thickness of the sharp focus plane your camera can capture (how is it called then?)...
... the thickness in reality, not in the picture.

...There is no such thing as an 'objective' DoF...

Do we need a new definition here? Because I'm pretty sure that OP was asking about THAT THING, not the CoC.

The plane of focus has no depth. Imagine it as a sheet of the thinnest paper, only much thinner. Everything in front of, and behind, that sheet of paper is less sharp than whatever is on the sheet of paper. Because of limitations to our eyesight something very close to the paper might look in focus, but it isn't, at some point as you move towards the paper things become more obviously out of focus, you have now surpassed your DoF/CoC criteria, but, step back and you again can't see the differences because your eyesight can't resolve it.

I agree that the focus plane of an optical image projection is thinner than it looks like. That's what the CoC thing is all about. However, the sensor resolution is limited and it has it's smallest possible dot size which is a pixel and which is a constant for a given camera.

Maintain a reproduction size and viewing distance ratio such that the CoC (point at which you can't see the difference between a point and a circle) and you can go as big, or as small, as you'd like.

No, you cannot do that. It could only apply to a camera with an infinite number of pixels. If a pixel is too big, then it becomes a square. If it's too small, then it disappears.
In all my statements I assumed that both FF and APSC sensors had the same pixel pitch. Otherwise, even the same format cameras (same sensor size) with different megapixel numbers (like 12 vs 36) should have different DoF/CoC characteristics.

Forget pixels, they have absolutely nothing to do with this conversation. If you have a sensor with very few pixels (none of us do) then it would be incapable of rendering our plane of focus without jaggies/steps. Similarly if you had a 100mp ff sensor it would just resolve your CoC better, it wouldn't make anything "sharper" or "more in focus" or change the size of the CoC. The DoF and CoC calculations do not care if your equipment is up to the task. Just like they don't need lens resolution capabilities to calculate their figures.

The DoF and CoC figures are just as applicable when you look through your viewfinder, where there are no pixels, as when you look at an output image.

Of course you can do that! That is the whole point. Go look in a TV store at the 1080 HD displays, stand 4 feet away from a 60" screen, now do the same to a 24" screen. The 24" screen looks sharper. Stand back so the 60" screen appears as big as the 24" screen did from 4 feet, bang, the 60" screen looks as sharp as the 24" screen did. The 60" screen has much bigger pixels so you need to view it from further away so it appears as a seamless image not a collection of dots.
Title: Re: How (and why) does sensor size change DOF?
Post by: Pi on July 19, 2013, 11:38:11 AM
The truth is, two photographers standing next to each other, one crop sensor, the other ff sensor, with exactly the same camera settings and the same framed image (meaning the crop owner has a wider lens), if they both take an image then the crop sensor image has more dof.

We are going in circles. Read my first post in this thread. "Same settings" does not make much sense. Do you consider 50/2 and 80/2 to be "the same settings"? Yes or No? What about 50/2 and 80/3.2? Are they "the same"? How do you exactly choose "the same settings" if the FL's must be different? You are confused by "f/2" without understanding that this is just a ratio. The meaningful thing to do is to shot not with the "same settings" but with the settings which would give you the same picture in terms of AOV, DOF, shutter speed and shot noise. Those are the equivalents settings. So in your scenario, the crop camera owner would choose, say, 50/2 to match 80/3.2, if that is possible. The problem is, sometimes it is not.

Quote
Or, consider the corollary of your statement "But the fact remains: smaller formats do not allow you to get deeper DOF.", that would be, larger formats do not allow you to shoot narrower dof.

Oh, no, this is not a corollary of my statement.
Title: Re: How (and why) does sensor size change DOF?
Post by: privatebydesign on July 19, 2013, 11:57:10 AM
More semantics.

Reread the second answer in this thread, on page one, and its two links, they contain the points you have made, even, in the equivalence link, the superfluous "some lenses don't exist".

With regards equivalence, yet again, crop cameras are far more limiting with the lenses we actually have available than ff cameras are.
Title: Re: How (and why) does sensor size change DOF?
Post by: Pi on July 19, 2013, 01:29:24 PM
Reread the second answer in this thread, on page one, and its two links, they contain the points you have made, even, in the equivalence link, the superfluous "some lenses don't exist".

That is the whole point, actually. The next question would be: why don't they exist, when they do not.

This is not semantics, it is an attempt to honestly answer the OP question, especially the (and why) part.
Title: Re: How (and why) does sensor size change DOF?
Post by: Meh on July 19, 2013, 02:17:59 PM
This is only an illusion of sharpness. The truth is what really matters (the information). Looking at the print from far away only proves that human vision is very limited. At close-up you can see all the information captured by your camera, both sharp and blurry parts. So, sharpness = information. Then from the distance you see much much less information despite that it looks sharper. This kind of sharpness ≠ information. This trick is about the CoC of your eyes, DoF has nothing to do with it.

As I pointed out previously, you appear to be confused about what DoF is.  As neuro just pointed out... DoF is not an objective paramater.  It is entirely subjective by definition.  It is the distance in front of and behind the plane of focus that appears sharp to a human observer.  There are implicit assumptions in the DoF derivation about viewing size, viewing distance, and visual acuity of the observer.

The only truth is that only the plane of focus is sharp.  And it's only maximally sharp not perfectly sharp.  Every plane in front of and behind is less sharp.  How much less sharp depends on a few things.  Whether you can see that it's less sharp depends on how big the print is, how far you are from it, and how good your eye sight is.

For you to say at this point in the thread "that only proves that human vision is very limited" suggests you are still fundamentally missing the point that DoF is in fact a function of the limitations in human vision.
Title: Re: How (and why) does sensor size change DOF?
Post by: CarlTN on July 19, 2013, 02:23:57 PM
Hey guys,
I've read it multiple times now and i really dont understand it. Why does the sensor size affect the DOF and why do FF cameras have a smaller DOF? Seems like a pretty basic question but i really couldn't wrap my head around this concept.

Greetings from Germany,
Knut Skywalker

I have to say, that is one hell of a name!!  Did your father fight in the clone wars, and also have rage issues?

This thread has drawn out all the optics nerds, I see.  Jolly good show!  It's a shame with all your collective knowledge, you can't go out and collectively build me a custom lens.
Title: Re: How (and why) does sensor size change DOF?
Post by: Wild on July 20, 2013, 04:40:42 AM
Yes, the same area, as a percentage of the total image area. That is where your enlargement and viewing distance come in. Enlarge a point and it gets bigger and more obvious until it is a circle, but it stays the same size in relation to the image as a whole. CoC is just about setting a standard about the distance at which a sharp point becomes a blurred circle to a humans eye, you cannot take the human eye out of the equation because the very definition of DoF contains the words "acceptably sharp" or "beyond the resolution of the human eye". That is a subjective element that is generalised to 0.2mm at 25cm in the final output. Obviously if we stand back our eyesight becomes the limiting factor so we can increase the CoC.

Maintain a reproduction size and viewing distance ratio such that the CoC (point at which you can't see the difference between a point and a circle) and you can go as big, or as small, as you'd like.

Wow that makes soooo much more sense now. I don't know why it was so hard for me to grasp that DOF is a subjective quality of a photo, which is highly dependent upon the human eye. Thanks for taking the time to provide the great explanations and descriptions!
Title: Re: How (and why) does sensor size change DOF?
Post by: Marsu42 on July 20, 2013, 07:47:13 AM
Wow that makes soooo much more sense now. I don't know why it was so hard for me to grasp that DOF is a subjective quality of a photo, which is highly dependent upon the human eye.

Welcome to the club :-> ... my guess is that often we talk about "hard" nerd/tech stuff which is a nice distraction and sometimes very helpful if you need specific advice. But over all that, the elephant in the room gets overlooked, meaning that so much about photography is "soft", subjective and relative. The only time this regularly surfaces is if someone is cornered in an argument and states something beyond the original point like "Well, but a good photog can shoot great images with a 10d and tech details don't matter anyway."
Title: Re: How (and why) does sensor size change DOF?
Post by: CarlTN on July 20, 2013, 02:00:22 PM
Wow that makes soooo much more sense now. I don't know why it was so hard for me to grasp that DOF is a subjective quality of a photo, which is highly dependent upon the human eye.

Welcome to the club :-> ... my guess is that often we talk about "hard" nerd/tech stuff which is a nice distraction and sometimes very helpful if you need specific advice. But over all that, the elephant in the room gets overlooked, meaning that so much about photography is "soft", subjective and relative. The only time this regularly surfaces is if someone is cornered in an argument and states something beyond the original point like "Well, but a good photog can shoot great images with a 10d and tech details don't matter anyway."

Good point.  And I assume somewhere in this thread, someone has mentioned how the depth of field always looks deeper via your eye through the viewfinder, than what the image sensor sees?  There's probably a name for this phenomenon.  (It's at least partly due to the fact that your eye has its own iris, along with the eye's "imager" not being the same size as the camera's...and probably a host of other factors.)  I didn't notice this as much before I started using sensors larger than aps-c.  Oddly enough the first time I really noticed it was with my 58mm f/1.4 on the 1D4, a 1.3x crop camera.  This is why it's almost impossible to manually focus a fast aperture lens accurately...especially if you're just using the standard focusing screen, and the distances are closer than 10 feet or so.

However, none of this brilliance you all are imparting, is getting the lens I want, designed.  60-110mm f/0.7 zoom w/4 stop multi-axis IS, painted metallic pearl white...with 14,000 months/ no interest...one day only sale!  (The day they're only open half the day...and no web orders taken during closed hours...etc...)
Title: Re: How (and why) does sensor size change DOF?
Post by: bdunbar79 on July 20, 2013, 03:14:23 PM
DOF is subjective?  Hmm.  If my DOF is 8 feet in a photo, that is, 8 real-life feet out in the field, how in the world does that ever change after I take the photo??  8 feet is 8 feet isn't it? 

Actually, I wouldn't even need to take the photo.  The DOF is still 8 feet.  :)

Are you suggesting that by being subjective, it could be 8 feet, or 6 feet, or 10 feet, or 7.23838383 feet?  How silly.
Title: Re: How (and why) does sensor size change DOF?
Post by: privatebydesign on July 20, 2013, 03:42:33 PM

Are you suggesting that by being subjective, it could be 8 feet, or 6 feet, or 10 feet, or 7.23838383 feet?  How silly.

Look at my two images on the previous page. On the top picture the zip is sharp, it comfortably falls inside DoF calculators range. In the bottom image it clearly is not in focus. The DoF has changed due to the reproduction size. Increase your viewing distance to make the big zip the same size in your fov that the little zip was and it becomes sharp again. From across the room the 46" print is razor sharp, put your face up in it and it still is, just less of it.

DoF is a figure based on aperture and subject magnification. If you magnify your subject more (increase your output size) you reduce DoF, just like in my two images.
Title: Re: How (and why) does sensor size change DOF?
Post by: bdunbar79 on July 20, 2013, 04:05:22 PM

Are you suggesting that by being subjective, it could be 8 feet, or 6 feet, or 10 feet, or 7.23838383 feet?  How silly.

Look at my two images on the previous page. On the top picture the zip is sharp, it comfortably falls inside DoF calculators range. In the bottom image it clearly is not in focus. The DoF has changed due to the reproduction size. Increase your viewing distance to make the big zip the same size in your fov that the little zip was and it becomes sharp again. From across the room the 46" print is razor sharp, put your face up in it and it still is, just less of it.

DoF is a figure based on aperture and subject magnification. If you magnify your subject more (increase your output size) you reduce DoF, just like in my two images.

Ok, I get it.  Thanks.
Title: Re: How (and why) does sensor size change DOF?
Post by: neuroanatomist on July 20, 2013, 05:05:50 PM
DOF is subjective?  Hmm.  If my DOF is 8 feet in a photo, that is, 8 real-life feet out in the field, how in the world does that ever change after I take the photo??  8 feet is 8 feet isn't it? 

Actually, I wouldn't even need to take the photo.  The DOF is still 8 feet.  :)

Are you suggesting that by being subjective, it could be 8 feet, or 6 feet, or 10 feet, or 7.23838383 feet?  How silly.

It seems you think that based on your equipment, there's a 'slice' of the photo that's in perfect focus, say 3.8 feet in front of where you focused, and 4.2 feet behind it, then WHAM like magic at 4.3 feet behind the focal plane, everything gets blurry.  That's not how it works.

Light from the plane of focus (which is best approximated by a plane in the geometric sense - 2D and infinitely thin) is focused on the image sensor (we're ignoring field curvature, of course).  Everything outside that plane, even a few millimeters, is blurry...and the further from the focal plane, the blurrier it gets. That's optical physics.  Whether it looks blurry to you depends on viewing size and distance and your visual acuity.

Tell me - how do you know your hypothetical shot has that 'real' 8 foot DoF?  Did you use a DoF calculator?  That calculator determines the 8 foot DoF based on an assumed specific print size and viewing distance (commonly 8x10" viewed at 1 foot).  Change those assumptions, you change the calculated DoF.
Title: Re: How (and why) does sensor size change DOF?
Post by: CarlTN on July 20, 2013, 05:32:21 PM

Are you suggesting that by being subjective, it could be 8 feet, or 6 feet, or 10 feet, or 7.23838383 feet?  How silly.

Look at my two images on the previous page. On the top picture the zip is sharp, it comfortably falls inside DoF calculators range. In the bottom image it clearly is not in focus. The DoF has changed due to the reproduction size. Increase your viewing distance to make the big zip the same size in your fov that the little zip was and it becomes sharp again. From across the room the 46" print is razor sharp, put your face up in it and it still is, just less of it.

DoF is a figure based on aperture and subject magnification. If you magnify your subject more (increase your output size) you reduce DoF, just like in my two images.

For a 46 inch print to look sharp with your face against it, is that 300 dpi?  What prints so large at 300 dpi?
Title: Re: How (and why) does sensor size change DOF?
Post by: privatebydesign on July 20, 2013, 06:11:11 PM

For a 46 inch print to look sharp with your face against it, is that 300 dpi?  What prints so large at 300 dpi?

I print at 240dpi, but don't get me started on peoples preconceptions on print resolution and how printer software dithers dots  :)

I shot it with a 1Ds MkIII and a 100mm L Macro at f7.1. Native resolution is 3744 x 5616, I then re-sampled it in one go (I did all the tests in PS years ago and one step re-size works best for me) to 7488 x 11232, that prints at 240 dpi to 31.2" x 46.8", the tiff is 84.1MB, exactly four times the size of the .CR2.

Here is a 700 x 700 px crop from the eye and eyebrow, to get a better idea of the print in person zoom your browser so it is just under 3" square, or print it out at 240dpi. Obviously at this size and viewing distance dof becomes minute, you can see it fall off even in the hairs less than an inch off the eye.

That is what we can do with 21mp cameras, and that is why I, personally, don't need or want more MP when they inevitably come around.
Title: Re: How (and why) does sensor size change DOF?
Post by: CarlTN on July 20, 2013, 06:22:18 PM

For a 46 inch print to look sharp with your face against it, is that 300 dpi?  What prints so large at 300 dpi?

I print at 240dpi, but don't get me started on peoples preconceptions on print resolution and how printer software dithers dots  :)

I shot it with a 1Ds MkIII and a 100mm L Macro at f7.1. Native resolution is 3744 x 5616, I then re-sampled it in one go (I did all the tests in PS years ago and one step re-size works best for me) to 7488 x 11232, that prints at 240 dpi to 31.2" x 46.8", the tiff is 84.1MB, exactly four times the size of the .CR2.

Here is a 700 x 700 px crop from the eye and eyebrow, to get a better idea of the print in person zoom your browser so it is just under 3" square, or print it out at 240dpi. Obviously at this size and viewing distance dof becomes minute, you can see it fall off even in the hairs less than an inch off the eye.

That is what we can do with 21mp cameras, and that is why I, personally, don't need or want more MP when they inevitably come around.

That's a nice picture and illustration of your point.  However, I recently did a 20x30 print scaled to 9000x6000 for 300dpi, shot with my 6D, with the 40mm pancake lens closed to f/9, ISO 100.  (Native resolution of the file before resizing, was slightly below the 6D's native due to minor cropping after correcting some lens distortion and adding some vertical angle correction of the shot.)  I was rushed at the last minute so I didn't perform a final noise reduction after some subtle sharpening done to the enlarged image.  After the print was done, I couldn't see any of the noise visible on the 9000x6000 file when I viewed it at 100%.  I concluded that the print could very likely have been done at 240dpi, rather than 300 (good thing this was only done on the cheap).  I can certainly still see the difference between 240 and 300 when I view from less than 1 foot away...and obviously it makes more difference at the smaller 20x30 size, than it would with a 46 inch wide print...because it has been scaled less of a percent above the native.

Did you use the standard "bicubic" in photoshop when you scaled it up?  I've found it works best, where "bicubic smoother" (claimed to work best for enlargement)...only adds softness to everything.  Even better is Perfect Resize 7, but I didn't even bother using it on this most recent 20x30.
Title: Re: How (and why) does sensor size change DOF?
Post by: privatebydesign on July 20, 2013, 07:59:30 PM
For smaller prints I'll print at higher dpi, indeed I never downsample, but for the big stuff I found 240 dpi to be perfectly fine, people don't literally put their nose on a 46" print, I found, like you, much more than 12"-20" viewing distance and the difference between 240 and 300 (I actually never use 300, but 320 after getting recommendations direct from Epson pro printers support re the printers native sampling figures of 720) becomes moot, though it can depend heavily on the printer paper and the subject matter.

Also, printing takes some detail out, so I won't remove so much noise for a print and will sharpen more when compared to an electronic output.

I don't remember which resample mode I used, I normally try a couple, I watched a great PS tutorial by Deke on Lynda.com a long time ago and he very nicely demonstrated files where the recommended method just broke down, so going on his suggestion I'll try two or three and see which works better for that particular image.

Hope this all helps.
Title: Re: How (and why) does sensor size change DOF?
Post by: bdunbar79 on July 20, 2013, 08:13:44 PM
DOF is subjective?  Hmm.  If my DOF is 8 feet in a photo, that is, 8 real-life feet out in the field, how in the world does that ever change after I take the photo??  8 feet is 8 feet isn't it? 

Actually, I wouldn't even need to take the photo.  The DOF is still 8 feet.  :)

Are you suggesting that by being subjective, it could be 8 feet, or 6 feet, or 10 feet, or 7.23838383 feet?  How silly.

It seems you think that based on your equipment, there's a 'slice' of the photo that's in perfect focus, say 3.8 feet in front of where you focused, and 4.2 feet behind it, then WHAM like magic at 4.3 feet behind the focal plane, everything gets blurry.  That's not how it works.

Light from the plane of focus (which is best approximated by a plane in the geometric sense - 2D and infinitely thin) is focused on the image sensor (we're ignoring field curvature, of course).  Everything outside that plane, even a few millimeters, is blurry...and the further from the focal plane, the blurrier it gets. That's optical physics.  Whether it looks blurry to you depends on viewing size and distance and your visual acuity.

Tell me - how do you know your hypothetical shot has that 'real' 8 foot DoF?  Did you use a DoF calculator?  That calculator determines the 8 foot DoF based on an assumed specific print size and viewing distance (commonly 8x10" viewed at 1 foot).  Change those assumptions, you change the calculated DoF.

Remember when I said this:

"Ok, I get it.  Thanks."

Sorry neuro, I couldn't resist  ;D :D :) ;) :P
Title: Re: How (and why) does sensor size change DOF?
Post by: ecka on July 21, 2013, 02:24:18 AM
DOF is subjective?  Hmm.  If my DOF is 8 feet in a photo, that is, 8 real-life feet out in the field, how in the world does that ever change after I take the photo??  8 feet is 8 feet isn't it? 

Actually, I wouldn't even need to take the photo.  The DOF is still 8 feet.  :)

Are you suggesting that by being subjective, it could be 8 feet, or 6 feet, or 10 feet, or 7.23838383 feet?  How silly.

It seems you think that based on your equipment, there's a 'slice' of the photo that's in perfect focus, say 3.8 feet in front of where you focused, and 4.2 feet behind it, then WHAM like magic at 4.3 feet behind the focal plane, everything gets blurry.  That's not how it works.

Light from the plane of focus (which is best approximated by a plane in the geometric sense - 2D and infinitely thin) is focused on the image sensor (we're ignoring field curvature, of course).  Everything outside that plane, even a few millimeters, is blurry...and the further from the focal plane, the blurrier it gets. That's optical physics.  Whether it looks blurry to you depends on viewing size and distance and your visual acuity.

Tell me - how do you know your hypothetical shot has that 'real' 8 foot DoF?  Did you use a DoF calculator?  That calculator determines the 8 foot DoF based on an assumed specific print size and viewing distance (commonly 8x10" viewed at 1 foot).  Change those assumptions, you change the calculated DoF.

So here we go. Once that optical physics hits the sensor it's no longer optical, it's information. The sensor cannot capture the infinitely thin plane of focus made of sharp points. Instead, it captures everything between the two distances where "a circle" has the size of a pixel or smaller, so everything in that range is same sharp, because there can't be anything sharper than a pixel. At that level, enlarging the image isn't going to decrease the DoF, only soften it, because there is no hidden information.
How do we call THAT THING? The sharpest area between the two distances where "a circle" meets the pixel?
Title: Re: How (and why) does sensor size change DOF?
Post by: Wild on July 21, 2013, 04:22:18 AM
So here we go. Once that optical physics hits the sensor it's no longer optical, it's information. The sensor cannot capture the infinitely thin plane of focus made of sharp points. Instead, it captures everything between the two distances where "a circle" has the size of a pixel or smaller, so everything in that range is same sharp, because there can't be anything sharper than a pixel. At that level, enlarging the image isn't going to decrease the DoF, only soften it, because there is no hidden information.
How do we call THAT THING? The sharpest area between the two distances where "a circle" meets the pixel?

Hey Ecka, I was in a similar state of skepticism here for a while so I just want to help get you where I am now using some common sense.

Forget all the technical stuff about aperture and sensor size for a second and let's just think about this from a simpler perspective. Imagine we just took a picture of a friend. You look at the picture later at 100% on your 30" computer monitor and realize that you accidentally focused on their nose, so their eyes are slightly out of focus. Wouldn't you agree that the plane of focus is on the nose, but doesn't extend to the eyes? Yes of course.

Now let's imagine the friend we took the photo of wants to post that photo to Facebook, and so you post it and it becomes their new profile photo. The whole time you're thinking man that photo wasn't even in focus, but then you go onto their Facebook page, and voila, nobody can even tell if their eyes are in focus because the photo's so small. Basically, the photo looks great. Now I think we can agree that as far as we can tell, their profile picture is in focus. Which would mean that either:

A. You uploaded the wrong picture
B. Magic
C. Our DOF changed because we're now looking at a much smaller picture

And just in case you're not sure. It's obviously B.   ;D
Title: Re: How (and why) does sensor size change DOF?
Post by: studio1972 on July 21, 2013, 05:18:22 AM
DOF is subjective?  Hmm.  If my DOF is 8 feet in a photo, that is, 8 real-life feet out in the field, how in the world does that ever change after I take the photo??  8 feet is 8 feet isn't it? 

Actually, I wouldn't even need to take the photo.  The DOF is still 8 feet.  :)

Are you suggesting that by being subjective, it could be 8 feet, or 6 feet, or 10 feet, or 7.23838383 feet?  How silly.

It seems you think that based on your equipment, there's a 'slice' of the photo that's in perfect focus, say 3.8 feet in front of where you focused, and 4.2 feet behind it, then WHAM like magic at 4.3 feet behind the focal plane, everything gets blurry.  That's not how it works.

Light from the plane of focus (which is best approximated by a plane in the geometric sense - 2D and infinitely thin) is focused on the image sensor (we're ignoring field curvature, of course).  Everything outside that plane, even a few millimeters, is blurry...and the further from the focal plane, the blurrier it gets. That's optical physics.  Whether it looks blurry to you depends on viewing size and distance and your visual acuity.

Tell me - how do you know your hypothetical shot has that 'real' 8 foot DoF?  Did you use a DoF calculator?  That calculator determines the 8 foot DoF based on an assumed specific print size and viewing distance (commonly 8x10" viewed at 1 foot).  Change those assumptions, you change the calculated DoF.

This is very correct. Before one can calculate DoF, one must first define what "in focus' actually means. A 300 pixel wide web image will have much more DoF than a 20MP version of the same original shot.

In answer to the original question, full frame sensors do generally allow more control over DoF than crop sensors, this is really to do with the lenses, as a 50mm 1.4 lens will have less DoF than a 35mm 1.4 lens (which is designed to do a similar field of view on a crop sensor based camera, all other things being equal.
Title: Re: How (and why) does sensor size change DOF?
Post by: neuroanatomist on July 21, 2013, 06:46:44 AM
Metaphorically speaking, it appears that many people are trapped within the circle of confusion, when it comes to discussions of DoF.

1. The formulas used to calculate DoF all contain CoC as a variable.
2. CoC is dependent on the observer's visual acuity, viewing distance, and output size.

Therefore,

3. DoF is dependent on the observer's visual acuity, viewing distance, and output size.

It's really that simple.

As for Ecka's argument about one pixel, the typically assumed values for CoC, and the practical range of CoC values for other print sizes and viewing distances, are much larger than a single pixel, so spatial quantization is not an issue.
Title: Re: How (and why) does sensor size change DOF?
Post by: ecka on July 21, 2013, 06:51:51 AM
So here we go. Once that optical physics hits the sensor it's no longer optical, it's information. The sensor cannot capture the infinitely thin plane of focus made of sharp points. Instead, it captures everything between the two distances where "a circle" has the size of a pixel or smaller, so everything in that range is same sharp, because there can't be anything sharper than a pixel. At that level, enlarging the image isn't going to decrease the DoF, only soften it, because there is no hidden information.
How do we call THAT THING? The sharpest area between the two distances where "a circle" meets the pixel?

Hey Ecka, I was in a similar state of skepticism here for a while so I just want to help get you where I am now using some common sense.

Forget all the technical stuff about aperture and sensor size for a second and let's just think about this from a simpler perspective. Imagine we just took a picture of a friend. You look at the picture later at 100% on your 30" computer monitor and realize that you accidentally focused on their nose, so their eyes are slightly out of focus. Wouldn't you agree that the plane of focus is on the nose, but doesn't extend to the eyes? Yes of course.

Now let's imagine the friend we took the photo of wants to post that photo to Facebook, and so you post it and it becomes their new profile photo. The whole time you're thinking man that photo wasn't even in focus, but then you go onto their Facebook page, and voila, nobody can even tell if their eyes are in focus because the photo's so small. Basically, the photo looks great. Now I think we can agree that as far as we can tell, their profile picture is in focus. Which would mean that either:

A. You uploaded the wrong picture
B. Magic
C. Our DOF changed because we're now looking at a much smaller picture

And just in case you're not sure. It's obviously B.   ;D

Thank you for trying, but I think the answer is F.

F. You are trying to answer a question I didn't ask.
F. "It doesn't matter" - is not an answer.
F. You don't need a DSLR for shooting thumbnails.
F. Now I know who uses the 720x480 small JPEG shooting format :).
F. Perhaps, my English is so bad, that nobody can understand what I'm saying :). Here's a picture:
(https://lh4.googleusercontent.com/-7dhhIgFyReQ/Ueu4k45x_hI/AAAAAAAADgc/1Y44H6DCheI/s705/omgwtf2013.jpg)
What is A-B?
Title: Re: How (and why) does sensor size change DOF?
Post by: ecka on July 21, 2013, 07:04:18 AM
Metaphorically speaking, it appears that many people are trapped within the circle of confusion, when it comes to discussions of DoF.

1. The formulas used to calculate DoF all contain CoC as a variable.
2. CoC is dependent on the observer's visual acuity, viewing distance, and output size.

Therefore,

3. DoF is dependent on the observer's visual acuity, viewing distance, and output size.

It's really that simple.

As for Ecka's argument about one pixel, the typically assumed values for CoC, and the practical range of CoC values for other print sizes and viewing distances, are much larger than a single pixel, so spatial quantization is not an issue.

I'm not asking about the illusion of sharpness, I'm asking about the information that camera can capture in the sharpest area.
Title: Re: How (and why) does sensor size change DOF?
Post by: neuroanatomist on July 21, 2013, 07:30:05 AM
I'm not asking about the illusion of sharpness, I'm asking about the information that camera can capture in the sharpest area.

Of course that's related to pixel size (but less spatial information than the pixel size suggests, due to AA filter effects, lens aberrations, etc.).

The question is, how do you define the 'sharpest area'?
Title: Re: How (and why) does sensor size change DOF?
Post by: ecka on July 21, 2013, 07:54:37 AM
I'm not asking about the illusion of sharpness, I'm asking about the information that camera can capture in the sharpest area.

Of course that's related to pixel size (but less spatial information than the pixel size suggests, due to AA filter effects, lens aberrations, etc.).

The question is, how do you define the 'sharpest area'?

Not all sensors have AA filters, not all are based on Bayer filter technology.
The sharpest area carries the highest amount of information about reality, compared to the rest of the image.
Title: Re: How (and why) does sensor size change DOF?
Post by: neuroanatomist on July 21, 2013, 08:09:18 AM
I'm not asking about the illusion of sharpness, I'm asking about the information that camera can capture in the sharpest area.

Of course that's related to pixel size (but less spatial information than the pixel size suggests, due to AA filter effects, lens aberrations, etc.).

The question is, how do you define the 'sharpest area'?

Not all sensors have AA filters, not all are based on Bayer filter technology.
The sharpest area carries the highest amount of information about reality, compared to the rest of the image.

True, but your definition is something of a tautology.  In terms of the real world being captured by the image sensor as sampled by the lens, how do you define 'sharpest area'?  Specifically, does that area have 'depth' relative to the sensor?  Pixel size represents the least quantifiable unit of XY resolution. What about Z-axis resolution?  After all, the latter is what this thread is about...
Title: Re: How (and why) does sensor size change DOF?
Post by: ecka on July 21, 2013, 12:08:11 PM
I'm not asking about the illusion of sharpness, I'm asking about the information that camera can capture in the sharpest area.

Of course that's related to pixel size (but less spatial information than the pixel size suggests, due to AA filter effects, lens aberrations, etc.).

The question is, how do you define the 'sharpest area'?

Not all sensors have AA filters, not all are based on Bayer filter technology.
The sharpest area carries the highest amount of information about reality, compared to the rest of the image.

True, but your definition is something of a tautology.  In terms of the real world being captured by the image sensor as sampled by the lens, how do you define 'sharpest area'?  Specifically, does that area have 'depth' relative to the sensor?  Pixel size represents the least quantifiable unit of XY resolution. What about Z-axis resolution?  After all, the latter is what this thread is about...

I suggest you to read all my posts in this thread, it might help to understand my position (if you didn't already).
Z-axis resolution? Where did that come from? The only thing that sensor gathers is the light to determine a color for each pixel. Everything else is just information manipulation. If you really don't understand how to define "the sharpest area", then you should study the principles of CDAF, it's all there.
Title: Re: How (and why) does sensor size change DOF?
Post by: Pi on July 21, 2013, 01:49:09 PM
Therefore,

3. DoF is dependent on the observer's visual acuity, viewing distance, and output size.

And, I would add, on how bad the observer's OCD is.

Quote
As for Ecka's argument about one pixel, the typically assumed values for CoC, and the practical range of CoC values for other print sizes and viewing distances, are much larger than a single pixel, so spatial quantization is not an issue.

Exactly. He is pushing the discussion into an extreme territory, where the usual (and reasonable) assumptions used to calculate DOF do not apply. If we really want to get there, "the plane of focus" is a bit ticker than a plane, actually. If he ever tried to MA an f/1.2 lens, he will understand what I mean. There is no single measure of sharpness and there is a whole range where the image appears kinda focused but not quite in different ways.
Title: Re: How (and why) does sensor size change DOF?
Post by: neuroanatomist on July 21, 2013, 02:08:47 PM
I suggest you to read all my posts in this thread, it might help to understand my position (if you didn't already).
Z-axis resolution? Where did that come from? The only thing that sensor gathers is the light to determine a color for each pixel. Everything else is just information manipulation. If you really don't understand how to define "the sharpest area", then you should study the principles of CDAF, it's all there.

I did read them, and it appears that you don't really understand what DoF is, or at least such understanding isn't coming across in your posts.  For example, "...CoC is about perception. DoF is not, it is about information..., and several iterations thereof.  That seems to sum up your argument, but that statement is fundamentally wrong. You cannot determine DoF without a CoC value, either arbitrarily chosen or empirically determined. DoF is based on CoC and other factors, so if you believe that you can determine DoF without CoC, you don't understand what DoF means.

As for 'the sharpest area', that's the focal plane, the plane in space at which the lens is focused. It's a plane, with effectively no depth (although practically, it has some - just as real lenses aren't the infinitely thin lenses we pretend they are for optical calculations).  Everything in front and behind that plane is less sharp, progressively more so at increasing distance along the optical axis. Whether or not regions outside the focal plane appear sharp...that's DoF, and it is affected by several factors, including CoC.
Title: Re: How (and why) does sensor size change DOF?
Post by: ecka on July 21, 2013, 05:23:09 PM
I suggest you to read all my posts in this thread, it might help to understand my position (if you didn't already).
Z-axis resolution? Where did that come from? The only thing that sensor gathers is the light to determine a color for each pixel. Everything else is just information manipulation. If you really don't understand how to define "the sharpest area", then you should study the principles of CDAF, it's all there.

I did read them, and it appears that you don't really understand what DoF is, or at least such understanding isn't coming across in your posts.  For example, "...CoC is about perception. DoF is not, it is about information..., and several iterations thereof.  That seems to sum up your argument, but that statement is fundamentally wrong. You cannot determine DoF without a CoC value, either arbitrarily chosen or empirically determined. DoF is based on CoC and other factors, so if you believe that you can determine DoF without CoC, you don't understand what DoF means.

As for 'the sharpest area', that's the focal plane, the plane in space at which the lens is focused. It's a plane, with effectively no depth (although practically, it has some - just as real lenses aren't the infinitely thin lenses we pretend they are for optical calculations).  Everything in front and behind that plane is less sharp, progressively more so at increasing distance along the optical axis. Whether or not regions outside the focal plane appear sharp...that's DoF, and it is affected by several factors, including CoC.

I understand the physics and if I don't quote books and articles, or post links for others to go read something, it doesn't mean that I don't understand a thing. I'm using my own head, because it is science, not a religion. Science provides tools, but you cannot use the same one for everything.
Does the CoC theory work for upscaling images? - No.
Are imaging sensors rendering DoF in a way you described - "a plane, with effectively no depth" where "everything in front and behind that plane is less sharp"? - No.
"Whether or not regions outside the focal plane appear sharp...that's DoF" - That applies to your eyes, not the original image. Think about it. It's like photographing a photograph.
End of the discussion ;).
Title: Re: How (and why) does sensor size change DOF?
Post by: neuroanatomist on July 21, 2013, 05:56:31 PM
"Whether or not regions outside the focal plane appear sharp...that's DoF" - That applies to your eyes, not the original image.

Yes, it still applies to the original image. Tell me...how do you calculate your (incorrect) concept of the "DoF" of 'the original image'.  I'd like to see the math behind that, if you could share it.  Also, what do you even call THAT THING - because it's not the DoF, by definition.

Regardless, while a tree falling in the forest with no one around to hear it does, in fact, make a sound, a photograph without someone to look at it is a completely meaningless collection of 0's and 1's or an equally meaningless collection of developed silver halide grains in an emulsion. The moment someone views it, all of my points about CoC apply...and that, for all purposes relevant to photographs, is the real end of the discussion.
Title: Re: How (and why) does sensor size change DOF?
Post by: ecka on July 22, 2013, 04:38:44 AM
"Whether or not regions outside the focal plane appear sharp...that's DoF" - That applies to your eyes, not the original image.

Yes, it still applies to the original image. Tell me...how do you calculate your (incorrect) concept of the "DoF" of 'the original image'.  I'd like to see the math behind that, if you could share it.  Also, what do you even call THAT THING - because it's not the DoF, by definition.

Regardless, while a tree falling in the forest with no one around to hear it does, in fact, make a sound, a photograph without someone to look at it is a completely meaningless collection of 0's and 1's or an equally meaningless collection of developed silver halide grains in an emulsion. The moment someone views it, all of my points about CoC apply...and that, for all purposes relevant to photographs, is the real end of the discussion.

Imagine that you are a cyborg and you see the world through cameras instead of eyes. One camera has 8mp APSC sensor from 20D and another one has 21mp FF sensor from 5D2 (yes, it's weird, you must be made in China, or something). Both with 40mm f/2.8 lenses. You see everything in clearest details up to a single pixel, all of them, all the time. FF camera has 60% wider FoV, but with both lenses focused at the same distance you would see that they both produce the same DoF.
This is a very simplified concept (no need to tell me that), because I don't want to waste any more time on this, but it is real and correct. That's how your camera sees it and renders the DoF. The question is not "How do my eyes deal with DoF?". It is "How the camera does it?". It may not be useful for thumbnails and snapshots, but there is a need for it in photography with extremely shallow DoF and a lot of cropping, like macro (where you can't bring it back if it's oof).
Title: Re: How (and why) does sensor size change DOF?
Post by: Hillsilly on July 22, 2013, 05:58:23 AM
My 2c...Choose your lens for DOF.  Choose your camera for framing. 

Now, for the revolutionary paradigm shift - you only ever need one lens.  You just have to carry a Pentax Q for getting in close, headshots etc , Nikon V1, a micro 4/3 camera, an APS-C camera, a FF camera, a medium format camera, and a large format camera for the wide angle work.  You'll also need a few adapters.  I'd suggest a 100mm lens.  DOF would be equivalent for all cameras, but you'd have a nice 16-550mm FF equivalence.
Title: Re: How (and why) does sensor size change DOF?
Post by: neuroanatomist on July 22, 2013, 07:17:31 AM
Imagine that you are a cyborg and you see the world through cameras instead of eyes. One camera has 8mp APSC sensor from 20D and another one has 21mp FF sensor from 5D2 (yes, it's weird, you must be made in China, or something). Both with 40mm f/2.8 lenses. You see everything in clearest details up to a single pixel, all of them, all the time. FF camera has 60% wider FoV, but with both lenses focused at the same distance you would see that they both produce the same DoF.
This is a very simplified concept (no need to tell me that), because I don't want to waste any more time on this, but it is real and correct. That's how your camera sees it and renders the DoF. The question is not "How do my eyes deal with DoF?". It is "How the camera does it?". It may not be useful for thumbnails and snapshots, but there is a need for it in photography with extremely shallow DoF and a lot of cropping, like macro (where you can't bring it back if it's oof).

Seriously?  A cyborg?  Sure, the DoF from the same lens, with the shot taken at the same distance and aperture but two different sensor formats, will have the same DoF.  While true (and something quite obvious that doesn't require a preposterous story to illustrate), it's irrelevant.  They yield the same DoF, but what is that DoF?  Imagine you have been preserved as a plastinated cadaver for an exhibit at the 24th-and-a-half Century Body Worlds exhibit, and me the cyborg is staring at your outstretched hand.  Are your wide, strangely lifelike eyes rendered sharply enough to appear unblurred? 

The camera doesn't render DoF. DoF is based on 'acceptable sharpness' and only exists when an image is viewed, and thus viewing conditions like output size and viewing distance matter.

Sorry, but it's now obvious beyond doubt that you just don't understand the concept of DoF (and apparently haven't bothered to even read the definition of the term), so this really is a waste of time.