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Nesgran, I have quite a bit of gear, including full frame and a couple of crop bodies with different pixel densities. If I take a prime lens and mount it on a tripod, then attach a body and aim at a target arranged to show DOF, I don’t find any discernible difference in DOF between a full frame body and a crop body, at the same aperture. I also don’t find any discernible difference in DOF between crop bodies.
If I take an 8 mpx crop body and put it behind a lens aimed at a target, then change bodies, attaching a 21.5 mpx full frame body, I can drop both images into Photoshop, at the same scale, and the 8 mpx image will fit almost perfectly on top of the 21.5 mpx image, with the border all the way around, showing the area cropped off by the smaller sensor. If instead of attaching the full frame body, I attach an 18 mpx crop body, then both images “fit to screen” look the same but at 100% everything in the 18 mpx file is larger. That a greater photo site density results in a bigger image when played back at the same resolution, as the image from a less dense sensor, is the basis of digital zoom. I think the notion of a crop sensor causing magnification equivalent to the crop factor came about because Nikon was offering a 12.5 mpx full frame body and a 12.5 mpx crop body. The effect happened due to the smaller, more tightly packed photo sites, not the sensor dimensions. Since then, both Canon and Nikon have offered many sensors with different densities, and lately, Canon are the ones in sync with the 1.6 crop factor working as magnification factor since the 1Dx, 7D and a number of other offerings all have 18 mpx. Nikon is offering a 36 mpx sensor in the D800, so if you use that as the full frame reference, the lens will seem shorter if the image is taken with a D3100 or D90 and both images are viewed at 100%. Of course the same is true if you compare images taken with the D800 and D3 or D4, yet they are all full frame bodies.
Getting back to DOF, if you fit a full frame body on a lens, and take a photo, then change bodies and use a crop body on the same lens, DOF will change if you back up in order to fit the same view as you had with the full frame body. This is not the body causing a change in DOF, this is you moving the crop body and lens and getting a greater DOF because you increased the focus distance.
Check the DOF requirements section
Where would I find the DOF requirements section?