# DOF, DX vs FX; diffraction

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Since the D3 is coming up, something poped up in my head:

I recall reading somewhere that the diffraction limit for DX cameras is at f/13,

for 35mm however, it is at f/16. Actually, looking at the data at photozone.de,

there is a slight loss of resolution going from f/8 to f/11 already.

Concerning macro photogaphy, I suppose there is an optimal point where you get

the most depth of field while minimizing depth of field. I have borrowed a book

in the library somewhere showing the depth of field (in millimeters) for close

to 1:1 photography.

Anyway, here is a simple question: will I be getting more depth of field

shooting a DX camera at f/13 or an FX camera at f/16?

TIA

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Diffraction and depth of field are two separate features in an image. Diffraction reduces sharpness in an image, while depth of field refers to how much is in focus. As your aperture gets smaller, you gain depth of field, but will gradually loose sharpness. Personally, I don't use apertures smaller than f/11 (and even then, I hesitate to use f/11 except when absolutely necessary) because of the loss of sharpness diffraction introduces.

An easy why to see this in work, is to make two images. Choose a highly detailed subject and make two images using a tripod and cable release - one at f/8 and one at your smallest aperture (say f/22 to f/45, depending on the lens). You will ALWAYS find the f/8 image is sharper. However, if your subject is three dimensional, you will also see that the smaller aperture leads to more of the subject being in focus...it just won't be as crisp or detailed as the in focus sections of the image made at f/8.

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As I understand it, it's like this. (please correct me if I'm wrong)

When using a non DX lens the DOF is the same on both the DX and FX format cameras.

There is a perceived greater DOF on a DX camera because you are only seeing the center of the image.

For example if you stand in the same place and took a shot with an 18mm lens on a DX camera, to get the same FOV, you would use a 27mm lens on an FX camera. You get a greater DOF on the DX camera, not because of the format or the f stop, but because of the FOCAL LENGTH.

So, if you took the same shot with both cameras with the SAME LENS (a non DX one), and then put the DX image over the center of the FX image, both images will look exactly the same.

F13 is f13, and f16 is f16, and therefore f16 will always have a greater DOF then f13 regardless of which 35mm based format you use.

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Andy - not exactly. Read the article cited by Alan. On DX, you require less magnification for the same field of view, therefore greater depth of field. The key is magnification, not focal length, but yes, they are largely related. It's the same reason you can't get silky background blur with a digicam, and why your cell phone cam, with a teeny sensor, doesn't need to focus at all due to it's massive DOF.

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