Roy
Well-known member
Cropping changes angle of view and file size only.
Cropping and sensor size does mot change DOF - apart from a slight change from COC only distance and aperture effect DOF...
How does crop mode or cropping in post impact subject isolation/DOF?
- Thread starter bleirer
- Start date
If you would like to post, you'll need to register. Note that if you have a BCG store account, you'll need a new, separate account here (we keep the two sites separate for security purposes).
Cropping and sensor size does mot change DOF - apart from a slight change from COC only distance and aperture effect DOF...
Cropping changes angle of view and file size only.
Cropping and sensor size does mot change DOF - apart from a slight change from COC only distance and aperture effect DOF...
I think what was established from the discussion was that if you only cropped and left the crop at its cropped size and viewed it small relative to the uncropped version, then it would not affect DOF, but if you increased the size to view it side by side with the same sized uncropped image, then yes it would affect the DOF. The reason is that the dof is dependent on the circle of confusion, but the circle of confusion is dependent on the viewing size, the viewing distance, and our visual acuity. So when our viewing image size was enlarged after cropping then the blur was also enlarged.
Roy
Well-known member
Re-sizing does not change DOF - Depth of field is the area from closest in focus to furthest in focus.
Circle of confusion is constant for any sensor and only a minor part of the DOF.
DOF is calculated only on COC, distance and Aperture.
Re-sizing changes the sharpness of the whole image...
I'm sorry Roy but that's not accurate. Go to any text on DoF or any online DoF calculator and you'll see that if you keep every other parameter the same and only change sensor size (or crop area) the DoF definitely changes. And yes it's because the circles of confusion grow in size with the image resizing.Re-sizing does not change DOF - Depth of field is the area from closest in focus to furthest in focus.
Circle of confusion is constant for any sensor and only a minor part of the DOF.
DOF is calculated only on COC, distance and Aperture.
Re-sizing changes the sharpness of the whole image...
Basically the slightly out of focus points of light that render as circles of confusion grow substantially with the resizing step and the resulting DoF decreases. And by definition the DoF for a constant output image size is defined as the points where CoCs grow to a predefined size (e.g. 0.01") for a defined image size at a defined viewing distance.
Here's a comparison of DoF between a full frame and crop body camera with all other parameters including: focal length, aperture and distance to focal plane kept constant:
|
|
Cropping or shooting with a crop body sensor and resizing for comparison at constant output size definitely changes DoF and when all else is kept constant the DoF decreases in response to the CoCs increasing in size in the enlarging step. As posted at the beginning of this thread it gets more complicated when you talk about changing lens focal length to hold the field of view constant but still the process of cropping impacts DoF.
Last edited:
Re-sizing does not change DOF - Depth of field is the area from closest in focus to furthest in focus.
Circle of confusion is constant for any sensor and only a minor part of the DOF.
DOF is calculated only on COC, distance and Aperture.
Re-sizing changes the sharpness of the whole image...
Check out this post that quotes the photography life article explaining the reasons. It is an interesting article. I think it is that for something to be considered out of focus to our eyes the size of the blur has to be more than the COC, but the COC changes with image size and viewing distance. Strange but true I guess.
Post in thread 'How does crop mode or cropping in post impact subject isolation/DOF?' https://bcgforums.com/index.php?thr...mpact-subject-isolation-dof.16169/post-180407
Roy
Well-known member
Watch the video by "Gerald Undone"...
Roy
Well-known member
There's over a century of science and hard mathematics in defining DoF and the impact of media size. It was well understood by the engineers at Leica and photographers like Ansel Adams that shot on multiple formats (e.g. 8x10 sheet film vs 4x5 sheet film or 120 roll film). As shown above simply cropping while keeping everything else the same does change DoF and it is due to the step of resizing the outputs to a common comparison size.
Gerald's introduction of 'direct' vs 'indirect' factors impacting DoF in that video just adds confusion and as shown in the calculator results leads to misunderstanding. He's also conflating a lot of things discussed earlier in this thread like changing shooting position or changing lenses which does indeed muddy the waters.
Last edited:
Yeah, the Photography Life article breaks it down nicely and includes good references to support their conclusions: https://photographylife.com/sensor-...e-physical-focal-length-and-physical-f-number
This section is right on topic with this discussion:
This section is right on topic with this discussion:
4.3) Three examples of how a smaller sensor influences Depth of Field
Roy
Well-known member
Sounds Fair...
Nice video. At the very end, " so in summary, does aperture, focal length and sensor size affect your depth of field? yes, but only because...."
Everything he said agreed with the article, and with everything DR was saying, he just never addressed the question I asked, about staying in one place with all factors the same but cropping. He jumped right in to changing subject distance or focal length, etc. But skipped over staying in one place. Even the PL article said it depended on viewing the images at the same size. The dof calculator he referenced in the video showed the same thing. When you change from full frame to crop sensor but keep everything else the same, the DOF was less.
What did you think of the PL article?
Everything he said agreed with the article, and with everything DR was saying, he just never addressed the question I asked, about staying in one place with all factors the same but cropping. He jumped right in to changing subject distance or focal length, etc. But skipped over staying in one place. Even the PL article said it depended on viewing the images at the same size. The dof calculator he referenced in the video showed the same thing. When you change from full frame to crop sensor but keep everything else the same, the DOF was less.
What did you think of the PL article?
Last edited:
Roy
Well-known member
The Article seems to make several contradictions and outright mistakes...
Roy
Well-known member
You cant compare smartphone lenses with camera lenses.
The writer assumes changing the distance to make the images similar.
Quote: A 100mm lens set to f/2.8 on a Nikon FX camera (which has a crop factor of 1.0) gives you the same field of view and depth of field that a 50mm lens set to f/1.4 would on a μ4/3 camera (which has a crop factor of 2.0).
This works only if distance is changed.
I plugged those numbers into the field of view calculator linked below. I put in a crop of 1.0 at 10 feet at 100mm compared to a crop factor of 2 at 10 feet and 50mm and I got identical results for the angle of view for both.
What numbers do you come up with?
Camera Field of View Details and Calculator (FoV)
Calculator of Field of View of camera and lens, both the dimensional size of the Field Of View seen at a specified distance, and also Angle Of View.
www.scantips.com
Calson
Well-known member
Got quite a bit off the original question which was subject isololation with DOF settings. If I want to maximize subjects from the background there are multiple ways to accomplish this in addition to using a long focal length lens with a large aperture setting. But reduced DOF is the least effective way to accomplish this. If the background is busy and cluttered or there are bright areas in the frame the image is weakened regardless of the aperture of the lens.
Better to change your position and in so doing change the background. Moving to another side or getting higher or lower to the ground works better. The reason I favor smaller telephoto lenses is that when I do not need a tripod I can change my position with ease.
The advantage of a 45MP full frame camera is having more space around the subject so I have more options in post to cut out sections that pull the viewer's eye away from the subject. The trick is learning to see what is in the frame besides the subject and may cause problems with the image before the shutter is tripped.
Better to change your position and in so doing change the background. Moving to another side or getting higher or lower to the ground works better. The reason I favor smaller telephoto lenses is that when I do not need a tripod I can change my position with ease.
The advantage of a 45MP full frame camera is having more space around the subject so I have more options in post to cut out sections that pull the viewer's eye away from the subject. The trick is learning to see what is in the frame besides the subject and may cause problems with the image before the shutter is tripped.
That is a nice calculation, but if you use a 60 mm lens on the D850 and a 40 mm lens on the D500 to get the same field of view, you get still different results.
You can only see EXIF info for this image if you are logged in.
You can only see EXIF info for this image if you are logged in.
Bill
Absolutely, I mentioned changing focal lengths to accommodate for crop factor at the start of this thread. It gets confusing fast if you change: position, distance to focal plane, aperture, focal length of lens or combinations of them as well as considering crop vs full frame images but in the end cropping still impacts DoF though sometimes in nonintuitive ways as you change other things.
Last edited:
You certainly can, it's an optical lens with properties defined by the physics of optics sitting in front of a very small sensor. Of course you can compare the camera in a smartphone to a more traditional camera, after all it's still a camera.
The fact remains, contrary to your assertion, that cropping or shooting with a crop sensor camera impacts DoF as demonstrated clearly by the DoF calculator results posted above.
This old post on DPReview may clarify some questions on photographic equivalence. To have the same depth of view with different formats the diameter of the aperture size (in millimeters, not f/number) must be the same.
Roy
Well-known member
All I know that when I change the sensor size (the back) on my Hasselblad H the DOF does not change at all...
Roy
Well-known member
No the DOF or Hyperfocal does not change when I change camera backs.
I read the PhotographyLife article and it draws the same conclusions as an article that I referenced previously. If the Hasselblad user changes backs to use a a smaller format, the depth of field will be the same if he uses the same settings from the same position, e.g. f/8 with an 80 mm lens at 5 meters. The entrance pupil will be the same and so the DOF will be the same also, but the field of view will be different. To get the same field of view and depth of field after switching to a smaller format, the user would have to use a shorter focal lenghth and open up the diaphragm. it is all explained in the articles which are well worth reading criticaly. Unput from multipe sources and civil discussion has solved he contradictions. Goodd work by all (or most all)
Cheers,
Bill
Last edited: