f/stop question on Full frame vs crop frame question

[Todd Good]

Is it true on a crop body the f/stop gets multiplied as well? So if I'm shooting at 2.8 on a 1.6 crop, I'm really shooting at 5.6. Any help on this issue would help. Thanks

Todd

[DVS_WiNdz]

No, f/2.8 is f/2.8. The only thing that changes is depth of field.

[Todd Good]

Originally Posted by DVS_WiNdz

No, f/2.8 is f/2.8. The only thing that changes is depth of field.

So does FF have less DOF than a crop at the same f/stop?

[DVS_WiNdz]

Yes, full frame has less dof at the same f stop.
Here are some samples http://www.aminfoto.com/2007/12/cano...e-vs-crop.html

[basroil]

no, the lens characteristics do not change no matter what the crop, a 200mm 1.8 will have a dof of .02m at 2.5m no matter what. what happens is that as you crop the edges, you need to stand further back to have the same framing. when you move back, you get more dof.

[JeffreyG]

Originally Posted by Todd Good

So does FF have less DOF than a crop at the same f/stop?

Essentially yes, supposing that you are framing the shot the same with each camera.

Suppose you set up a shot on a FF body with an 80mm lens at f/4. They you take the same shot at f/4 from the same distance with a crop camera, but this time you change the lens focal length to 50mm.

These two shots will look the same, except the FF shot will have a shallower DOF because the lens used is longer.

DOF increases with
Shorter focal length
Smaller aperture
Closer focus distance

[n1as]

Originally Posted by Todd Good

Is it true on a crop body the f/stop gets multiplied as well? So if I'm shooting at 2.8 on a 1.6 crop, I'm really shooting at 5.6. Any help on this issue would help. Thanks

Todd

Crop factor has a lot of misinformation surrounding it. When you put a lens on a crop body, the crop factor does NOT change the lens focal length. The 50mm f/1.4 is still a 50mm f/1.4. Period. The lens focal length does not change.

Not.

The smaller sensor captures less of the image formed by the lens and therefore gives your image the field of view that is smaller, as if it were taken through a lens with a longer FL.

[penagate]

Magnification is the key variable affecting depth of field which most people seem oblivious to.

[Wilt]

A 100mm f/2 lens used on FF camera will indeed have a smaller DOF than a 60mm f/2 lens used on an APS-C camera...DOF 0.294' vs. DOF 0.52' at shooting distance of 10' to achieve the same framing.

But if you put a 100mm f/2 lens on both format cameras and stand at 10', the APS-C camera has less DOF at 0.184' vs DOF 0.294', because it has to be magnified by 1.6x more to make the same final print size !

If you move forward with the FF camera so that both frames have the same FOV with the same 100mm lens, the APS-C camera has greater DOF, at 0.18' vs. 0.10'.

[AJSJones]

Originally Posted by basroil

no, the lens characteristics do not change no matter what the crop, a 200mm 1.8 will have a dof of .02m at 2.5m no matter what.

Nope! DoF is not an intrinsic property of a lens any more than print size is an intrinsic property of the lens.

The degree of enlargement from the captured image to the print AND the viewing distance are both REQUIRED pieces of information BEFORE the CoC can be calculated. THEN, you need the appropriate CoC to use the DoF tables. The conventions (not NOT laws of physics!) before digital came along were based on something like a 35 mm frame, printed at ~8x12" (about 8x enlargement) viewed from ~15" derived from the observation that the human eye can commonly resolve 300 ppi under those conditions.

It has become murkier with digital if folks are printing at (e.g.) 300 ppi the print size and degree of enlargement is all over the place ; the 10D will give a 10 x7 print while the 1Ds3 will give a 18.7 x 12.5 " print, but these are 11.5x and 13.2x enlargements respectively - and who knows how closely they are scrutinized. Then there's 100% pixel peeping that's another 3-4 x enlargement. DoF is losing some of its credibility!

See also Post#10 in http://photography-on-the.net/forum/...d.php?t=467572 running concurrently on basically the same issue!

[Wilt]

Originally Posted by AJSJones

It has become murkier with digital if folks are printing at (e.g.) 300 ppi the print size and degree of enlargement is all over the place ; the 10D will give a 10 x7 print while the 1Ds3 will give a 18.7 x 12.5 " print, but these are 11.5x and 13.2x enlargements respectively - and who knows how closely they are scrutinized. Then there's 100% pixel peeping that's another 3-4 x enlargement. DoF is losing some of its credibility!

The CoC sizes are based upon the absolute resolution of the typical human eye to resolve tiny detail, and has NOTHING to do the dpi ppi or any other digital scaling. Assuming infinitely fine ability to reproduce details, the smallest detail perceived with the human eye can be described as an angular measurement which can be projected to a CoC size at a certain viewing distance.

[AJSJones]

Originally Posted by AJSJones

The degree of enlargement from the captured image to the print AND the viewing distance are both REQUIRED pieces of information BEFORE the CoC can be calculated. THEN, you need the appropriate CoC to use the DoF tables. The conventions (not NOT laws of physics!) before digital came along were based on something like a 35 mm frame, printed at ~8x12" (about 8x enlargement) viewed from ~15" derived from the observation that the human eye can commonly resolve 300 ppi under those conditions.

Originally Posted by Wilt

The CoC sizes are based upon the absolute resolution of the typical human eye to resolve tiny detail

Glad you agree with me!

Originally Posted by AJSJones

It has become murkier with digital if folks are printing at (e.g.) 300 ppi the print size and degree of enlargement is all over the place ; the 10D will give a 10 x7 print while the 1Ds3 will give a 18.7 x 12.5 " print, but these are 11.5x and 13.2x enlargements respectively - and who knows how closely they are scrutinized. Then there's 100% pixel peeping that's another 3-4 x enlargement. DoF is losing some of its credibility!

See also Post#10 in http://photography-on-the.net/forum/...d.php?t=467572 running concurrently on basically the same issue!

Originally Posted by Wilt

The CoC size ... NOTHING to do the dpi ppi or any other digital scaling. Assuming infinitely fine ability to reproduce details, the smallest detail perceived with the human eye can be described as an angular measurement which can be projected to a CoC size at a certain viewing distance.

The whole point I was making was that the digital world does NOT have the infinite ability to resolve fine details and many people will print their pixels to the max, without regard for their original geometric dimensions. You've seen the Threads on "how big can I print with a xxD?", so we have significant variations in degree of enlargement - and as you know - the CoC that is appropriate for calculating depth of field depends on that factor. Therefore we have significant variations in DoF. All of these have to be taken into account when some asks (either themselves or someone else) a question about DoF!