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08-17-2016, 11:03 AM   #1
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Crop Mode DoF Question

When using the crop mode on the K1 do you get the depth of field of a full frame sensor or of a crop sensor at the same aperture?

08-17-2016, 11:09 AM   #2
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No. DoF is a purely perceptual thing, so regardless of the way you crop:

If you keep the viewing size and distance the same, any cropping creates a deeper (worse?) DoF compared to a larger sensor/uncropped image *showing exactly the same frame*.

Fun fact: If you just crop and then enlarge to same viewing size (thus obviously changing the framed area), the perceived DoF actually is more shallow compared to your uncropped image on the same sensor size, as you magnify more and all magnification results in less DoF. --> cutting/cropping anything in post changes DoF.
08-17-2016, 11:15 AM - 1 Like   #3
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QuoteOriginally posted by SamuelDixon Quote
When using the crop mode on the K1 do you get the depth of field of a full frame sensor or of a crop sensor at the same aperture?
Assuming you don't change the aperture, if you don't move the camera and only switch the crop mode on and off, the depth of field will be identical. However, if you move the camera to keep the subject framed the same way between FF and crop, then the depth of field will change. As you move back due to the narrower FoV with a crop sensor, the DoF will be deeper.
08-17-2016, 12:23 PM   #4
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QuoteOriginally posted by beholder3 Quote
No. DoF is a purely perceptual thing, so regardless of the way you crop:

If you keep the viewing size and distance the same, any cropping creates a deeper (worse?) DoF compared to a larger sensor/uncropped image *showing exactly the same frame*.

Fun fact: If you just crop and then enlarge to same viewing size (thus obviously changing the framed area), the perceived DoF actually is more shallow compared to your uncropped image on the same sensor size, as you magnify more and all magnification results in less DoF. --> cutting/cropping anything in post changes DoF.
Great answer thanks!

---------- Post added 08-17-16 at 12:24 PM ----------

QuoteOriginally posted by enoeske Quote
Assuming you don't change the aperture, if you don't move the camera and only switch the crop mode on and off, the depth of field will be identical. However, if you move the camera to keep the subject framed the same way between FF and crop, then the depth of field will change. As you move back due to the narrower FoV with a crop sensor, the DoF will be deeper.
Very helpful, thanks!

08-17-2016, 04:06 PM   #5
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QuoteOriginally posted by SamuelDixon Quote
When using the crop mode on the K1 do you get the depth of field of a full frame sensor or of a crop sensor at the same aperture?
The word crop is used twice in this question. I believe it answers itself.


Steve
08-18-2016, 05:03 AM   #6
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QuoteOriginally posted by stevebrot Quote
The word crop is used twice in this question. I believe it answers itself.

Steve
Nope.
08-18-2016, 07:04 AM   #7
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QuoteOriginally posted by SamuelDixon Quote
Nope.
In crop mode the K-1 IS a crop sensor camera and all "rules" and conventions associated with the APS-C format apply, including DOF. There are implications in regards to the perception of DOF in the viewfinder as compared to that of say, the K-3II, but those do not affect the DOF in the final image.

So the answer to your question is, "For a given aperture you will get the DOF for a crop sensor".


Steve

Last edited by stevebrot; 08-18-2016 at 07:19 AM.
08-18-2016, 08:21 AM   #8
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QuoteOriginally posted by stevebrot Quote
In crop mode the K-1 IS a crop sensor camera and all "rules" and conventions associated with the APS-C format apply, including DOF. There are implications in regards to the perception of DOF in the viewfinder as compared to that of say, the K-3II, but those do not affect the DOF in the final image.

So the answer to your question is, "For a given aperture you will get the DOF for a crop sensor".


Steve
The two people who answered this question above seem to have a different opinion...

08-18-2016, 08:37 AM   #9
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As many have said, no, DOF doesn't change.
I believe the easiest way to explain it (or understand it, depending on which side of the conversation you're on) is this:
Start with a print. 8x10, 4x5, whatever, and with scissors cut some off of each edge. The DOF of the remaining image won't change.
08-18-2016, 09:10 AM   #10
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QuoteOriginally posted by Parallax Quote
As many have said, no, DOF doesn't change.
I believe the easiest way to explain it (or understand it, depending on which side of the conversation you're on) is this:
Start with a print. 8x10, 4x5, whatever, and with scissors cut some off of each edge. The DOF of the remaining image won't change.
You are right, but the whole thing really depends on a number of parameters. If you enlarge the cut out piece back to the original size (what usually happens on digital media like monitors) then the DoF goes down (like if you had used a smaller F-Number or larger! sensor).

Generally the word "change" here is misleading because the opening post was not about changing, but about a direct comparison and for this it is very important to also understand that the image frame itself must be kept equivalent.

Sounds like an easy question but is not easy to follow. I bet 3 out of 4 users don't understand it.
08-18-2016, 09:23 AM   #11
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QuoteOriginally posted by SamuelDixon Quote
The two people who answered this question above seem to have a different opinion...
I will not comment regarding other comments on this thread except to say that statements on this topic are generally correct, but also sometimes misleading or incomplete. I answered your question in as direct and accurate manner possible. Crop mode is a simple crop of the 24x36 format and equivalent to the same capture using the same lens, subject, and camera position as if it were taken with an APS-C body. Ditto for a crop in post-processing. As for DOF, I will elaborate below.

By definition DOF is the range of planes of focus where an observer will perceive acceptable sharpness in an image. The long answer regarding factors for calculation and "equivalence" goes something like this: DOF depends on the visual acuity of the observer, the final magnification of the displayed image (by convention to an 8x10 print), the absolute aperture (not f-number)*, and the viewing distance.** Because of the difference in magnification to attain the final image size, DOF varies by format/crop, all other variables being controlled.


Steve

* Absolute aperture is the diameter of the lens entry pupil. Relative aperture (written as f/n) is the ratio of the lens focal length to the absolute aperture expressed as a fraction (e.g. f-stop, f-number, f-ratio).

** This is all related to the ability of the eye to perceive detail. The nominal resolution of human vision at the fovea is about 1 minute of arc (1/60th of a degree).

Last edited by stevebrot; 08-18-2016 at 03:47 PM.
08-18-2016, 03:27 PM   #12
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QuoteOriginally posted by Tjompen1968 Quote
focus and then take an image i FF and one i crop, the DOF is the same.
Only if there is the same discrepancy in the final image size or if you crop the FF image in PP to the APS-C pixel dimensions. The images are fully equivalent at this point. The converse is easy enough to demonstrate by down sampling the FF image to the same pixel dimensions. FOV is not a factor nor is "framing", but magnification is. Or coming from the other direction, both my avatar image and the photo below were from the same APS-C capture. Which has the greater DOF? (Hint: The only difference is the magnification.)




Steve

Last edited by stevebrot; 08-18-2016 at 03:38 PM.
08-18-2016, 03:43 PM   #13
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QuoteOriginally posted by Tjompen1968 Quote
Check out the Tony Northrup videos on the subject on youtube.
A link would be helpful.

Edit: it is my understanding that Northrup asserts (quite properly) that images must be normalized for crop when calculating DOF.


Steve

Last edited by stevebrot; 08-18-2016 at 03:51 PM.
08-18-2016, 04:15 PM   #14
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QuoteOriginally posted by Tjompen1968 Quote
The DOF is the same for all sizes of sensors IF the focal length is the same, the aperture is the same and the subject distance is the same. So if you have your K-1 on a tripod with a certain lens on it and set the aperture and focus and then take an image i FF and one i crop, the DOF is the same.
I hate to beat this dead horse any longer, but it may help to consider that the concept of DOF is defined in terms of the subject space in front of the camera lens and the final image as perceived by the person viewing. In the subject space we have the point/plane of focus as well as an infinite number of planes both near and far from that point. There is a corresponding range of focus points/planes at the nominal focal plane, but only one of those becomes part of the capture (important). What is perceived in the final image is a more sharp image of things at the plane of focus and progressively less sharp images of those in the planes to front and rear. The ability to differentiate more from less sharp is related to the distance from the viewer such that as distance from viewer to image increases average sharpness approaches infinity.


Steve
08-18-2016, 04:21 PM - 1 Like   #15
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QuoteOriginally posted by Tjompen1968 Quote
Or we can answer the question the OP asked without digging for the 100:th decimal of pi.
No need. I (and one other commentator) answered the OP's question early on. The DOF is the same in crop mode as with a crop sensor camera.

As for your photos, you made my point nicely. Thanks!


Steve
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