Chuck Norcutt wrote:
> <snip>
>>> and the 5D sensor is diffraction limited beyond f/11.
>>>
>> That I haven't noticed, but it may be subtle at f16-22 and lost in other
>> factors like DOF, focal accuracy and motion.
>>
> If you haven't noticed softening at 16-22 he many not notice it either
> at 8-11. A test with some contrived really fine detail might be
> required since subtle loss of detail in real world images might not be
> noticed except by side-by-side comparison.
>
I was sitting out on a lounge chair in the sun reading today and this
huge, perfect dandelion head kept calling to me. So I decided to do a
little DOF vs. diffraction test. The least I could do for those still
recovering from the big NE storm.
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.
The camera was tripod mounted and manual focus was not changed during
each series. However, a light breeze came and went. I mostly waited for
still moments, but didn't worry too much, as shutter speeds were high.
In retrospect, subject movement may have changed the focus slightly.
That may explain why in one full pixel sample there is more change from
f16 to f22 than in the other, or not.
Canon 5D, Tamron 90/2.8 Macro.
OM content: This may mean no pixel diffraction effect on 4/3 size
sensors down to f11.
Moose
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