Thanks. Since I'm not sure I even have anything that goes to f/32
(maybe the 90mm Series 1 macro) I shall shoot with impunity... well, at
least until the 1:1 adapter is attached or the lens extension gets to
the point where marked apertures are no longer meaningful.
Chuck Norcutt
Moose wrote:
>
> Focused on the top face of the dandelion - cropped to just the head
> <http://www.moosemystic.net/Gallery/tech/PixelDiffraction/DandyTops.htm>.
>
> Focused on the top face of the dandelion - full pixel sample
> <http://www.moosemystic.net/Gallery/tech/PixelDiffraction/DandyTopfp.htm>.
>
> Focused about halfway between outer face and center - cropped to just
> the head
> <http://www.moosemystic.net/Gallery/tech/PixelDiffraction/DandyMids.htm>.
>
> Focused about halfway between outer face and center- full pixel sample
> <http://www.moosemystic.net/Gallery/tech/PixelDiffraction/DandyMidfp.htm>.
>
> My conclusion is that either this is another area where theory and
> practice differ or some of the assumptions that go into the calculator
> aren't true for the 5D.
>
> For DOF of a fairly deep close-up subject, the overall sharpness
> improves right down to f32. So for an 8x10 of the FF cropped slightly to
> just the head, and ignoring background bokeh, it appears f32 would give
> the best overall apparent sharpness due to greater DOF.
>
> At the full pixel level, I just can't see any loss of
> resolution/sharpness through f16. There may be a little loss at f22. One
> sample seems to show that and the other doesn't. It could even be that
> the area I focus my eyes on isn't right on the plane of focus. I could
> do another test on a flat subject, but as a practical matter, it doesn't
> matter, as the smaller apertures would only be used for 3D subjects
> where extra DOF is desired.
>
> My conclusion is that anything down to f22 on the 5D is unaffected in
> any practical way by pixel diffusion. F32 clearly loses sharpness. This
> test does not, however prove that that is only from pixel diffraction,
> it could also be due in some part to ordinary aperture diffraction. I
> know that the 135/4.5 macro lens has noticeably decreased sharpness on
> film at f45 and wouldn't be surprised if a test like this showed some
> effect at f32 as well.
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