Full frame, crop frame "crop factor," resolution, cropping etc

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Originally Posted by GrumpyDiver

One other "downside" of crop frame versus full-frame shooters is that you get a wider DoF, by around 1 stop with crop frame. In other words, shooting f/2.8 on a crop frame gives you roughly the same DoF that f/4 does on a full-frame.

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I've heard this stated before but never had it explained in technical terms. What does sensor size have to do with it? Isn't this another generalization that is in-fact a function of pixel density and related "circle of confusion"?

On Edit: Answered by Google. CoC is function of sensor size, not pixel density/photosite size :)

I've been meaning to check on the dof aspect. I suspect what is actually happening is that the depth of field increases when comparing the same angle of view compared with full frame. Taking M 4/3 the focal length will be 1/2 that of full frame. The shorter the focal length the deeper the depth of field. There is an answer to that after a fashion on m 4/3, 12mm F2, 45mm F1.8 and 75mm F1.8 primes. There isn't a fast zoom so far even though it would probably be easier to make than for larger sensors. On APS on Canon for instance there is an F2.8 medium FL zoom from memory with as would be expected has a fairly restricted range. I've not looked at Canon or Nikon primes.

John
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I think that the reason is that for the same FoV, the full frame camera is positioned closer to the subject than the crop frame camera is.

Full Frame and APS-C each have their devoted priesthoods on the various forums (or should that be forii) that I visit but by and large it all seems to come down to your preferred shooting style.

I love wide angle landscapes and I like working in low light so guess what I use.

A friend of mine mostly shoots birds in good light so guess what he uses.

In terms of image quality on the final results there is not much to choose but we wouldn't swap our cameras for the World.

Manfred, I believe that you are exactly correct...

1.

For the same angle of view; the crop camera format will provide a wider depth of field than the full frame format for the reason that you mentioned: you need to be closer with the full frame to get the same cropping. - That will result in a more narrow DOF with the full frame camera.
Or,
You need to use a longer focal length with the full frame camera if shooting from the same distance in order to get the image framed the same. As an example, if I am shooting with a 50mm lens at a certain distance with a crop camera, I would need to use an 80mm lens to get the same framing with a full frame camera - that will also result in a more narow DOF. This is one area in which the crop factor can be important...

HOWEVER

2.

If you are shooting with the same focal length, at the same f/stop and focused at the same distance - THE CROP WILL GIVE A MORE NARROW DOF...

Example:

I am shooting with a 1.6x crop camera at f/2.8 and focused at ten feet using a 50mm lens my DOF = 1.29 feet

I am shooting with a full frame camera at f/2.8 and focused at ten feet using a 50mm lens my DOF = 2.06 feet

In reality, I would either use a longer focal length or get closer to my subject if I were shooting with a full frame camera than I would if I were shooting with a crop camera; so in most cases that second scenario is a moot point.