I post too Much on Here!!
- Jul 21, 2010
Yes, f/2.8 is f/2.8 and the light per unit area of the sensor is the same, independent of sensor size. Likewise, the focal length of a lens doesn't change on crop vs. FF, just the angle of view (i.e. the magnification is the same). The effect on DoF is an apparent one, seen in practice, even with the same lens. If I frame a head shot with an 85mm f/1.2 @ f/1.2 on my 7D, then I say 'whoops, what am I thinking' and move the 85/1.2 onto a 5DII without moving my feet or the subject, instead of a nice, tight head shot I'll have a lot of background around the subject. So, I'll take a few steps forward to get that nice tight framing again, and that decreased distance-to-subject translates to a shallower DoF - by a factor of 1.6x.epsiloneri said:Ok, good, then I understand. You are right, that for the same lens the aperture doesn't change when you go from FF to crop. That would be weird. But now think of two different lenses that both share the same entrance pupil - say 18mm in both cases - but where the focal length is different, namely 50mm in one case and 31.25mm in the other.Flake said:So you don't agree that 50mm/2.8 on a FF is identical to 31.25mm/1.75 on 1.6 APS-C? Or is it something else?
Yes I don't agree with that, f/2.8 is f/2.8 regardless of the crop factor