OK, now I've read Roger's article... maybe even re-read it since it was
published almost 3 years ago. I think I have a much different take on
it (minus the deconvolution stuff). If you read his article closely,
when he says "diffraction ain't so bad" he is comparing resolution at
small apertures to resolution at max or near max apertures. He is not
comparing resolution at small apertures to resolution at optimum
apertures for minimizing diffraction.
In the theoretical optical world a lens at widest aperture should have
the optimal resolution. In the real optical world there are many more
optical gremlins that affect images at large apertures than at small
apertures. For example, take his results using the Nikon 50/1.4 on the
D3X. Average resolution is only about 325 at f/1.4. Maximum resolution
of about 810 occurs at f/8. But f/16 shows the effect of diffraction by
knocking resolution back down by about 25% to about 610. What Roger is
actually saying is that resolution of 610 looks pretty good compared to
325 wide open. You have to close down 3 stops to f/4 to even equal the
f/16 result. What his results do show is that diffraction has a very
real effect and starts taking its toll about where theory says it should.
I'm not sure why this stuff should be surprising. If I'm shooting at
f/1.4 - f/4 I'm probably shooting something like a portrait. Maximum
resolution is hardly my goal. If I'm a macro shooter I also (now, after
Moose has beat it into me) accept that increased depth of field can
often improve the overall image even though maximum resolution may not
be achieved at the point of focus. Where I really do want maximum
resolution is in landscapes where I'm probably using hyperfocal methods.
I've shot many more landscapes with the 5D than any other camera and
have always used f/11 as the aperture limit to avoid diffraction
effects. I have never found f/11 to be a limiting factor in nearest
focus with hyperfocal methods. In other words, I have found it to be
perfectly acceptable for total depth of field.
Where all of this stuff starts to break down in the field is the effect
of wind or vibration on "optimal" resolution. Or, after the fact, use
of sharpening methods to improve at least the appearance of greater
resolution. I don't know how to evaluate any of that numerically.
I've been perfectly happy shooting my landscapes using theoretically
derived diffraction limits and have no reason to change. In any case,
I've never been able to count the lines of resolution in trees or grass
or clouds and have no idea what's actually be achieved. It either looks
good or doesn't.
Chuck Norcutt
On 1/30/2016 11:17 PM, Mike Gordon via olympus wrote:
I would advise Dr. D. to stay away from hospitals and pay closer attention to
the list. :-)
My original link to his article was here:
http://lists.tako.de/html/Olympus-OM/2013-05/msg02068.html
To cut to the chase and Roger's article:
http://www.lensrentals.com/blog/2013/03/overcoming-my-fentekaphobia
The exact diffraction effects are further complicated by de-mosaicing
algorithms combine the output of multiple Bayer-arrayed photosites.
Ya can't get no less diffraction, but you can try, Mike
--
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