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Some shots with E-M1+40-150 & D810+70-200

Started Jan 17, 2015 | Discussions thread
forpetessake
forpetessake Veteran Member • Posts: 5,172
Re: Some shots with E-M1+40-150 & D810+70-200

Alan GR wrote:

This has probably been answered here somewhere before but I am new... I was wondering why does this actually happen, as in why does a lens at the equivalent focal length and same aperture produce a deeper dof on a smaller sensor? I shot with the Nikkor at 200mm f2.8 and the Zuiko at 100mm at f2.8 so I would get the same field of view. Is that what causes the dof difference? If I shot the Nikkor at 100mm and the Zuiko at 100mm, would I then get a different field of view but the same dof? I have not tried that. It is just interesting to me... Thanks.

You can check the formulas, e.g. in Wikipedia, or just play with a DOF calculator. It's easy to see that DOF scales very well with the crop factor for the lenses with the same FOV. The same happens with the shot noise. That's why scaling the aperture proportionally to the crop factor produces the equivalent images (same FOV, same DOF, same shot noise).

Interesting corollary of the equivalent calculations is that for a given FOV at the same DOF you get the same shot noise and v.v. independent of the camera format -- it's the lens physical aperture that defines both. So the format wars are pretty much misguided -- it's not about the sensors, the real question is whether there are equivalent lenses and what quality those are.

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