About DOF on FX vs DX

Started 4 months ago | Discussions thread
VBLondon Contributing Member • Posts: 626
Re: About DOF on FX vs DX

beatboxa wrote:

The misconception of DX having a deeper DoF comes when people use equivalent focal length but not equivalent F-number. In other words, a 150mm F/4 FX lens vs. 100mm F/4 DX lens. The latter actually has a smaller aperture, and the two are not 'equivalents' other than in field of view. A true 150mm F/4 FX lens would have a DX equivalent closer to 100mm F/2.8--and these would provide similar field of view, depth of field, noise performance, etc.

Thanks, let me ask an additional question.

It's sometimes said that smaller formats are better when you need maximum DoF. Am I right in thinking that diffraction limits the max DoF in an equivalent way? Eg. In the example above, if the max DoF I can get from my 100mm f4 or f2,8 DX lens is at f11 (above which I am unhappy at the diffraction, just as an illustration) then I'd get the same max DoF and same amount of diffraction at f16 with the FX 150/2,8.

Therefore, "greater DoF" is not ever a benefit of a smaller format? All that can be said is that the option of shallower DoF that larger formats offer is not something that an individual might ever need?

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