Good exemples of the DoF difference between FF and crop.

Feel free to post your own samples!! But if I remember well, the results while using a same lens were just as dramatic.

Here is a fairly technical explanation of the difference between crop & FF DOF. I read through the entire article one afternoon. It sold me on adding a FF to my bag and also gave me a headache... Enjoy!

http://www.graphic-fusion.com/fullframe.h​tm#dof

Might be a good idea to also explain/show how you can achieve the same results with each format...

http://www.have-camera-will-travel.com …ame_vs_crop_sen​sor_-.html

Earwax69 wrote in post #14934721
Here a test made on Nikon that show the DoF difference between equivalent situations (50mm on crop, 85mm on FF, 85 on crop, 135 on ff)

http://tonycorrea.com …portrait-lens-comparison/

Have fun!

I'd be very interested to see the results if you had the same lens on both cameras, set at the same aperture, and cropped the full frame image down to the same field of view as the crop.

Tiberius47 wrote in post #14936971
I'd be very interested to see the results if you had the same lens on both cameras, set at the same aperture, and cropped the full frame image down to the same field of view as the crop.

As far as DoF is concerned, the results would be the same as none of the factors affecting DoF would be different: subject distance, focal length, and f ratio are of course identical. The only other factor, the circle of confusion, would be rendered identical by using sensors of the same size in every practical sense given the cropping undertaken.

xarqi wrote in post #14936019
Like most of these analyses, it demonstrates the effect of differences in focal length on DoF, not the effect of differences in format.

(Yes, I'm doing it again.)

Or is it the effect of different aperture sizes at the same framing?

"Framing" isn't an optical or physical property; it is totally subjective. Whatever framing the user chooses is implemented by selecting the appropriate focal length for the format in use (or by cropping in post-processing).

Even if you generalise "framing" to mean "captured angle of view", you end up in the same place, with the selection of the appropropriate focal length for the given format.

As such, any invocation of "framing" as a cause immediately devolves to the more fundamental concepts of focal length and format.

DreDaze wrote in post #14935156
i would've liked to have seen 50mm on a crop, and then 50mm on a FF moved forward to obtain the same framing

Hello - I am the original poster of the comparison in question. The testing performed was primarily with portraiture using medium telephoto lenses in mind. Changing the camera to subject distance would change the perspective of the image. Hence the test shots were taken at the same subject distance instead of moving the camera to match exact subject magnification. In addition to apparent depth-of-field, moving the FF 50mm to match the DX 50mm view, you would have a different, relatively slightly wider angle look to the FF image.

Tiberius47 wrote in post #14936971
I'd be very interested to see the results if you had the same lens on both cameras, set at the same aperture, and cropped the full frame image down to the same field of view as the crop.

Hi - I am the original poster of the comparison in question. A 50mm lens is a 50mm lens is a 50mm lens no matter what body you attach it to. If the image is taken from the same position with the exact same lens at the same aperture/focus point, a FF image cropped to match a smaller sensor image area would yield the same depth-of-field. The only difference would be down to the difference sensors in camera (noise, detail, etc).

A crop sensor camera does just that - crop the image relative to a 35mm FF image capture. A 35mm FF frame is cropped relative to a medium format 645 camera. The 645 image is cropped relative to a 4x5 camera. An so on.

tcstudios wrote in post #14937415
Hello - I am the original poster of the comparison in question. The testing performed was primarily with portraiture using medium telephoto lenses in mind. Changing the camera to subject distance would change the perspective of the image. Hence the test shots were taken at the same subject distance instead of moving the camera to match exact subject magnification. In addition to apparent depth-of-field, moving the FF 50mm to match the DX 50mm view, you would have a different, relatively slightly wider angle look to the FF image.

Welcome at P.O.T.N.

At least one more person understand here what "stepping back" isn't really practical solution.

This is another practical method to see the difference between cropper and FF:
http://www.dofmaster.c​om/dofjs.html

xarqi wrote in post #14937035
As far as DoF is concerned, the results would be the same as none of the factors affecting DoF would be different: subject distance, focal length, and f ratio are of course identical. The only other factor, the circle of confusion, would be rendered identical by using sensors of the same size in every practical sense given the cropping undertaken.

tcstudios wrote in post #14937457
Hi - I am the original poster of the comparison in question. A 50mm lens is a 50mm lens is a 50mm lens no matter what body you attach it to. If the image is taken from the same position with the exact same lens at the same aperture/focus point, a FF image cropped to match a smaller sensor image area would yield the same depth-of-field. The only difference would be down to the difference sensors in camera (noise, detail, etc).

A crop sensor camera does just that - crop the image relative to a 35mm FF image capture. A 35mm FF frame is cropped relative to a medium format 645 camera. The 645 image is cropped relative to a 4x5 camera. An so on.

So both of you are saying what I've always believed - the difference in DoF on a fullframe compared to a cropper isn't because of the different sensor size, but due to the fact you need to move the camera to get the same framing.

Tiberius47 wrote in post #14937543
So both of you are saying what I've always believed - the difference in DoF on a fullframe compared to a cropper isn't because of the different sensor size, but due to the fact you need to move the camera to get the same framing.

Give the man a cigar! But, I think there is a little more to it!

xarqi wrote in post #14937169
"Framing" isn't an optical or physical property; it is totally subjective. Whatever framing the user chooses is implemented by selecting the appropriate focal length for the format in use (or by cropping in post-processing).

Even if you generalise "framing" to mean "captured angle of view", you end up in the same place, with the selection of the appropropriate focal length for the given format.

As such, any invocation of "framing" as a cause immediately devolves to the more fundamental concepts of focal length and format.

Framing is certainly a physical property, as is perspective. It can be measured. It incorporates specific placement of subjects in the frame at the same angle of view. Perspective maintains the relationship in size between those subjects. To equalize testing for differences between format, you would have to use the same framing and perspective. Otherwise, you have changed more than one variable and your test is invalid.

Now we know that longer focal lengths have shallower DOF from the same distance. But why? Is it because the aperture size is larger for longer focal lengths at the same f-ratio? I tend to think it is.

For example:

1.6x crop with 85mm f4 from 10 feet = 0.62 feet of DOF.
85mm/4 = 21.25mm aperture size
FF with 135mm at 10 feet has same perspective and framing as 85mm on APS-C. 135mm with 21.25mm aperture = f6.35
FF with 135mm lens at f6.35 = 0.62 feet of DOF.

But, if you set the 135mm lens of FF to f4, now you have a 33.75mm aperture. I'd argue that is the real reason for the DOF change, not the focal length. If we increased the aperture of the crop camera to 33.75mm, you'd end up with the same DOF on the 85mm lens.

Of course at some point, you run out of room on the APS-C combo because max aperture size of the longer lens is going to be larger. So that is where the advantage for the larger sensor begins.

Tiberius47 wrote in post #14937543
So both of you are saying what I've always believed - the difference in DoF on a fullframe compared to a cropper isn't because of the different sensor size, but due to the fact you need to move the camera to get the same framing.

Consider this, shooting a 3' tall subject...

50mm f/4 on FF at distance of 10' captures an area of 4.7' x 7.1' in the frame, and the DOF zone is 2.4'
50mm f/4 on APS-C at distance of 15.9' captures an area of 4.7' x 7.1' in the frame, and the DOF zone is 3.87'

The subject in the frame is identically sized as a percentage of the frame height in both shots. The FL and aperture are identical for both shots. The DOF is different. So it seems to support your conjecture about distance.

But if we also consider this...

50mm f/4 on FF at distance of 10' captures an area of 4.7' x 7.1' in the frame, and the DOF zone is 2.4'
31.5mm f/4 on APS-C at distance of 10' captures an area of 4.7' x 7.1' in the frame, and the DOF zone is 3.94'

The distance in this case is identical, but the DOF zone is different! So distance cannot be the ultimate causative agent of DOF difference.

Tiberius47 wrote in post #14937543
So both of you are saying what I've always believed - the difference in DoF on a fullframe compared to a cropper isn't because of the different sensor size, but due to the fact you need to move the camera to get the same framing.

I'm expecting SkipD to come in here and link his sticky any moment, but in his absence:

What you posted doesn't really hold up in comparing DoF differences between crop and full frame.

For any comparison to be "fair", the subject distance should be a constant. As soon as you move in closer, your foreground subject might be framed the the same size, but your background will become wider, so you will have a different composition.
If you move further away with a long lens, the DoF will appear to become more narrow, but that's an effect of the smaller relative amount of your background in the frame.

Everyone in doubt of the effects of this should really try to take some shots of a subject with a clear background at various distances and focal lengths and try to frame the foreground the same size.