November 28, 2014, 01:11:11 AM

Author Topic: How (and why) does sensor size change DOF?  (Read 28281 times)

neuroanatomist

  • CR GEEK
  • **********
  • Posts: 14984
    • View Profile
Re: How (and why) does sensor size change DOF?
« Reply #90 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.
EOS 1D X, EOS M, and lots of lenses
______________________________
Flickr | TDP Profile/Gear List

canon rumors FORUM

Re: How (and why) does sensor size change DOF?
« Reply #90 on: July 17, 2013, 11:04:18 PM »

ecka

  • 5D Mark III
  • ******
  • Posts: 687
  • Size matters ;)
    • View Profile
    • flickr
Re: How (and why) does sensor size change DOF?
« Reply #91 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
FF + primes !

BozillaNZ

  • EOS M2
  • ****
  • Posts: 161
    • View Profile
Re: How (and why) does sensor size change DOF?
« Reply #92 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.
Look ma, me cameraz can push shadow 10 stoops w/o noizes, OMGWTFBBQChickenwingHaxorz!!!11
www.flickr.com/photos/bozillanz/

Matthew19

  • PowerShot G1 X II
  • ***
  • Posts: 56
    • View Profile
Re: How (and why) does sensor size change DOF?
« Reply #93 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)

Marsu42

  • Canon EF 400mm f/2.8L IS II
  • *******
  • Posts: 5122
  • ML-66d / 100L / 70-300L / 17-40L / 600rts
    • View Profile
    • 6D positive spec list
Re: How (and why) does sensor size change DOF?
« Reply #94 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.


Sporgon

  • Canon EF 300mm f/2.8L IS II
  • *******
  • Posts: 2047
  • 5% of gear used 95% of the time
    • View Profile
    • www.buildingpanoramics.com
Re: How (and why) does sensor size change DOF?
« Reply #95 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.

Sporgon

  • Canon EF 300mm f/2.8L IS II
  • *******
  • Posts: 2047
  • 5% of gear used 95% of the time
    • View Profile
    • www.buildingpanoramics.com
Re: How (and why) does sensor size change DOF?
« Reply #96 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.


canon rumors FORUM

Re: How (and why) does sensor size change DOF?
« Reply #96 on: July 18, 2013, 07:55:43 AM »

neuroanatomist

  • CR GEEK
  • **********
  • Posts: 14984
    • View Profile
Re: How (and why) does sensor size change DOF?
« Reply #97 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. 
EOS 1D X, EOS M, and lots of lenses
______________________________
Flickr | TDP Profile/Gear List

Pi

  • 1D Mark IV
  • ******
  • Posts: 937
    • View Profile
    • Math and Photography
Re: How (and why) does sensor size change DOF?
« Reply #98 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?
« Last Edit: July 18, 2013, 04:28:12 PM by Pi »

privatebydesign

  • Canon EF 300mm f/2.8L IS II
  • *******
  • Posts: 2781
  • Ermintrude says "moo"
    • View Profile
Re: How (and why) does sensor size change DOF?
« Reply #99 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
  • Crop camera: 200mm, f2, 100iso
  • FF camera: 320mm, f3.2, 200iso


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".
Never look down on anybody, unless you are helping them up.

Pi

  • 1D Mark IV
  • ******
  • Posts: 937
    • View Profile
    • Math and Photography
Re: How (and why) does sensor size change DOF?
« Reply #100 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.

privatebydesign

  • Canon EF 300mm f/2.8L IS II
  • *******
  • Posts: 2781
  • Ermintrude says "moo"
    • View Profile
Re: How (and why) does sensor size change DOF?
« Reply #101 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.
Never look down on anybody, unless you are helping them up.

Pi

  • 1D Mark IV
  • ******
  • Posts: 937
    • View Profile
    • Math and Photography
Re: How (and why) does sensor size change DOF?
« Reply #102 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?

canon rumors FORUM

Re: How (and why) does sensor size change DOF?
« Reply #102 on: July 18, 2013, 04:53:08 PM »

privatebydesign

  • Canon EF 300mm f/2.8L IS II
  • *******
  • Posts: 2781
  • Ermintrude says "moo"
    • View Profile
Re: How (and why) does sensor size change DOF?
« Reply #103 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.
Never look down on anybody, unless you are helping them up.

Sporgon

  • Canon EF 300mm f/2.8L IS II
  • *******
  • Posts: 2047
  • 5% of gear used 95% of the time
    • View Profile
    • www.buildingpanoramics.com
Re: How (and why) does sensor size change DOF?
« Reply #104 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

canon rumors FORUM

Re: How (and why) does sensor size change DOF?
« Reply #104 on: July 18, 2013, 05:53:55 PM »