Full Frame Vs Crop Sensor

[Skulker]

I saw that before.. but what really threw me today is the one guy claiming that focal length doesn't affect dof... maybe I read it wrong.. but ugh.

Focal length can affect DoF - it just depends on what else you do or do not hold constant. If you change focal length without changing subject distance, you're changing DoF. If you change subject distance without changing focal length, you're changing DoF. In each case, you're changing the magnification - the size of the subject. But if you keep the size of the subject constant (e.g., move closer as the focal length gets shorter), then DoF remains constant for a given aperture - that's why the statement that DoF depends on magnification and aperture is a better way to phrase it.

Put another way, DoF is determined by magnification and aperture, and magnification is determined by focal length and subjet distance.

A lot of people seem to have difficulty grasping this concept. Including some who think they know better in this thread. ;D Its shown quite well in this article.

http://www.luminous-landscape.com/tutorials/dof2.shtml

I don't see how the context of the article would contradict anything said in this thread.

The article studies "zooming by feet", while keeping the same sensor format.

The thread discusses changing sensor formats, while keeping the perspective intact.

I'm not sure if you are thinking that I claimed or implied that "the context of the article would contradict anything said in this thread". Au contraire what I was saying was that some people don't seem to grasp this simple relationship, the subject of the article I linked to. It is rather counter intuitive and many people have not grasped the link. I thought the article was a good clear explanation that restricted itself to a relevant and concise description, without going of at a tangent into irrelevant areas as so many do. It was jdramirez who questioned what someone had said. (and pleased don't read that to be a criticism of jdramirez from my point of view he was just asking for clarification and there is nothing wrong with that.)

 

[Cory]

If it helps with the discussion - tried a Sigma 18-35 yesterday at a workshop on my 70D and was thoroughly blown away. So thoroughly that I ordered one today.

 

[candc]

If it helps with the discussion - tried a Sigma 18-35 yesterday at a workshop on my 70D and was thoroughly blown away. So thoroughly that I ordered one today.

Its a smashing lens, the best one I have but I never use it because I always seem to shoot ultrawide or super telephoto, I just don't seem to use the mid fl much, if you do then this is the best one there is for aps-c.

 

[jdramirez]

I'm not sure if you are thinking that I claimed or implied that "the context of the article would contradict anything said in this thread". Au contraire what I was saying was that some people don't seem to grasp this simple relationship, the subject of the article I linked to. It is rather counter intuitive and many people have not grasped the link. I thought the article was a good clear explanation that restricted itself to a relevant and concise description, without going of at a tangent into irrelevant areas as so many do. It was jdramirez who questioned what someone had said. (and pleased don't read that to be a criticism of jdramirez from my point of view he was just asking for clarification and there is nothing wrong with that.)

I'm still wrapping my head around all of this. I was under the impression that dof was dictated by aperture, distance to your subject, and focal length... and then there is the full frame v. crop... where full frame has a slightly more dof field all things being equal... but if focal length isn't a factor... well...

And then I was reading something about shooting video a few months back... and they made a point that instead of shooting at 35 or 40mm on a zoom lens... use the larger depth of field when @ 24mm and you don't have to worry about dof as much.

But if I'm framing my subjects identically... then that advice is flawed.

And there are so many (what feels like differing opinions) opinions from people whose opinions I respect... that it is hard to say what is or is not accurate. Do I trust this person... or this person... or neither...

I'm just going to say screw it and shoot everything at minimum focusing distance and wide open. I don't care if all of my subjects are in focus... seriously... what do they expect... not to be blurry?

 

[ahab1372]

A lot of people seem to have difficulty grasping this concept. Including some who think they know better in this thread. ;D Its shown quite well in this article.

http://www.luminous-landscape.com/tutorials/dof2.shtml

Note that no where in the luminous landscape article did the guy refer to subject isolation.

DOF and subject isolation (or background blur - or do you mean something else?) are not necessarily the same.
Taking pictures with a short focal length and short subject distance vs with a long focal length and longer subject distance (for the same framing, using the same camera and aperture) results in the same dof, but the latter will give you a much blurrier background.

 

[Kit.]

I'm not sure if you are thinking that I claimed or implied that "the context of the article would contradict anything said in this thread".

Content, sorry, but anyway.

Au contraire what I was saying was that some people don't seem to grasp this simple relationship, the subject of the article I linked to. It is rather counter intuitive and many people have not grasped the link.

Well, it's probably counter intuitive because it's wrong in general. It only works when the distance to the subject is much shorter than hyperfocal.

I thought the article was a good clear explanation that restricted itself to a relevant and concise description, without going of at a tangent into irrelevant areas as so many do.

The article itself belongs to an irrelevant area. It's a piece of trivia that is good to know when you choose a lens for your macro work (DoF vs. background separation), but it has nothing to do with the subject of this thread.

 

[ecka]

"Wide open" vs "wide open" is pointless.

I see your point, but I beg to differ concerning the conclusion: If you want the thinnest dof (or fastest speed) with any lens/camera combination you'll use "wide open" a lot in reality, so it's perfectly valid to look at this performance no matter the synthetic equivalence.

Look? - yes. Compare? - no. If you want the thinnest dof, then you should get a FF camera in the first place. The fact that 10-22 can't do f/1.8 (which is the FF equivalent for f/2.8 ) doesn't justify your logic. There is no f/1.8 UWA for APSC (for now, maybe the mighty Sigma will make one later ) and that's another reason to go FF.

 

[ecka]

A lot of people seem to have difficulty grasping this concept. Including some who think they know better in this thread. ;D Its shown quite well in this article.

http://www.luminous-landscape.com/tutorials/dof2.shtml

Note that no where in the luminous landscape article did the guy refer to subject isolation.

DOF and subject isolation (or background blur - or do you mean something else?) are not necessarily the same.
Taking pictures with a short focal length and short subject distance vs with a long focal length and longer subject distance (for the same framing, using the same camera and aperture) results in the same dof, but the latter will give you a much blurrier background.

How about - "For the same magnification of the area in focus (different lenses, different distances), longer focal length at the same aperture will give you same DoF and more background magnification".

 

[ahab1372]

A lot of people seem to have difficulty grasping this concept. Including some who think they know better in this thread. ;D Its shown quite well in this article.

http://www.luminous-landscape.com/tutorials/dof2.shtml

Note that no where in the luminous landscape article did the guy refer to subject isolation.

DOF and subject isolation (or background blur - or do you mean something else?) are not necessarily the same.
Taking pictures with a short focal length and short subject distance vs with a long focal length and longer subject distance (for the same framing, using the same camera and aperture) results in the same dof, but the latter will give you a much blurrier background.

How about - "For the same magnification of the area in focus (different lenses, different distances), longer focal length at the same aperture will give you same DoF and more background magnification".

Yes. Or, in simple statements, which I can remember easier :
The longer the lens at the same f, the more blur, but same dof.
The smaller the f at the same mm, the more blur, and less dof.
(assuming the same framing)

 

[Sporgon]

A lot of people seem to have difficulty grasping this concept. Including some who think they know better in this thread. ;D Its shown quite well in this article.

http://www.luminous-landscape.com/tutorials/dof2.shtml

Note that no where in the luminous landscape article did the guy refer to subject isolation.

DOF and subject isolation (or background blur - or do you mean something else?) are not necessarily the same.
Taking pictures with a short focal length and short subject distance vs with a long focal length and longer subject distance (for the same framing, using the same camera and aperture) results in the same dof, but the latter will give you a much blurrier background.

How about - "For the same magnification of the area in focus (different lenses, different distances), longer focal length at the same aperture will give you same DoF and more background magnification".

Yes. Or, in simple statements, which I can remember easier :
The longer the lens at the same f, the more blur, but same dof.
The smaller the f at the same mm, the more blur, and less dof.
(assuming the same framing)

My point is that the article deals with pure theory of one aspect, sets up an experiment to prove that theory, ( correctly ) but then does nothing to put this into practical context, creating the real possibility of leaving someone who is new to photography, but trying to learn, more confused about what they find in practice.

That's all. There are people who post on CR who are better at putting pure physics into practical context.

 

[ahab1372]

My point is that the article deals with pure theory of one aspect, sets up an experiment to prove that theory, ( correctly ) but then does nothing to put this into practical context, creating the real possibility of leaving someone who is new to photography, but trying to learn, more confused about what they find in practice.

That's all. There are people who post on CR who are better at putting pure physics into practical context.

True, someone new to photography might wonder "what's the point?". I haven't read a lot on LL, but my feel is that that is true for most of their articles.

 

[privatebydesign]

It is just magnification and aperture, once you accept that, however convoluted the route to getting there, then it is easier on the mind.

Start to think magnification and aperture and all the inconsistencies and complications fall away.

 

[ecka]

It is just magnification and aperture, once you accept that, however convoluted the route to getting there, then it is easier on the mind.

Start to think magnification and aperture and all the inconsistencies and complications fall away.

Well, there are other things involved in "magnification" which are not taken into account by most people who are trying to learn how things actually work, so it may be an oversimplification. This rule may not work that well when shooting something farther away, because UWA lenses would go hyperfocal, while the tele lens would still produce some blur in the background (due to stronger magnification) and that's the rare situation when the CoC thing becomes important before you actually take a picture. You have to take the convoluted route first, and then, if you survive , you can calculate using the magnification and aperture, because you'll know the exceptions.

 

[privatebydesign]

So the only important bit is to educate people on the apparently simple concept of magnification.

At the very essence of all this is:

1. How big is the object as you now see it in relation to how big it is in real life.
2. How big was the aperture opening.

The first allows for everything involved in the reproduction; focal length, distance to object, coc, sensor size, crop, print or screen size, and viewing distance. Each of those affects the magnification. Plugging these values into a dof calculator just allows it to calculate the magnification taking the print or screen size and viewing distance as standards for a set CoC, some calculators actually allow you to change the CoC and magically your DOF changes, even though the image is already taken.

The second dictates the amount of blur in relation to the magnification.

Hyperfocal is a side issue with no merit, stuff falling within the hyperfocal is still not as sharp as the plane of focus. magnify it the same and it is just as blurred (try it with the images on the LL link, I did for a thread a long time ago). Indeed lenses marked hyperfocal scales are historically at least one stop wider than accepted norm CoC figures because they used a different value to calculate them. But the important bit is that hyperfocal is just another manifestation of magnification, it isn't sharp, it is just small enough to give the illusion of sharp.

 

[sdsr]

I'm just going to say screw it and shoot everything at minimum focusing distance and wide open. I don't care if all of my subjects are in focus... seriously... what do they expect... not to be blurry?

http://www.27bslash6.com/photography.html

 

[jdramirez]

I'm just going to say screw it and shoot everything at minimum focusing distance and wide open. I don't care if all of my subjects are in focus... seriously... what do they expect... not to be blurry?

http://www.27bslash6.com/photography.html

I enjoyed that very much.

 

[ecka]

So the only important bit is to educate people on the apparently simple concept of magnification.

At the very essence of all this is:

1. How big is the object as you now see it in relation to how big it is in real life.
2. How big was the aperture opening.

The first allows for everything involved in the reproduction; focal length, distance to object, coc, sensor size, crop, print or screen size, and viewing distance. Each of those affects the magnification. Plugging these values into a dof calculator just allows it to calculate the magnification taking the print or screen size and viewing distance as standards for a set CoC, some calculators actually allow you to change the CoC and magically your DOF changes, even though the image is already taken.

The second dictates the amount of blur in relation to the magnification.

Hyperfocal is a side issue with no merit, stuff falling within the hyperfocal is still not as sharp as the plane of focus. magnify it the same and it is just as blurred (try it with the images on the LL link, I did for a thread a long time ago). Indeed lenses marked hyperfocal scales are historically at least one stop wider than accepted norm CoC figures because they used a different value to calculate them. But the important bit is that hyperfocal is just another manifestation of magnification, it isn't sharp, it is just small enough to give the illusion of sharp.

It is all about the illusion of sharp. The actual plane of focus is always at it's thinest, which is the diffraction limit of a lens. However, when the CoC becomes as small as a single pixel of your camera sensor, it is perfectly sharp from that point and smaller. That's how you gain the depth (of field ). You will cross the line when it is impossible to magnify it enough, because the resolution is too low.

 

[Northstar]

It is just magnification and aperture, once you accept that, however convoluted the route to getting there, then it is easier on the mind.

Start to think magnification and aperture and all the inconsistencies and complications fall away.

PBD....you're right, i had always thought of the three.... focal length, distance to subject, aperture....but when i read what you wrote, "start to think magnification and aperture" only....you're right, it's easier to think of it that way.

thanks,
north

 

[privatebydesign]

It is just magnification and aperture, once you accept that, however convoluted the route to getting there, then it is easier on the mind.

Start to think magnification and aperture and all the inconsistencies and complications fall away.

PBD....you're right, i had always thought of the three.... focal length, distance to subject, aperture....but when i read what you wrote, "start to think magnification and aperture" only....you're right, it's easier to think of it that way.

thanks,
north

Glad it helped, t least one person.