Perhaps this post is at least of interest to Dr. Diffraction and Moose:
Moose has always said that stopping down for dof if required for
the image even past the diffraction threshold should usually be done
though maximal sharpness in the in focus areas may be slightly
compromised. When aperture bracketing when I was previously more
nervous going way past the sweet spot for a lens, empirically the dof
gain almost always offset
the modest diffraction softening (as I don my I agree with
MooseT--shirt) unless the image is turned to mush at very small
apertures. Spotted this more exacting review of the situation :
http://www.lensrentals.com/blog/2013/03/overcoming-my-fentekaphobia
To quote Roger at Lensrentals from the link:
"The message I took away, though, is that diffraction softening is
real, it occurs where it is supposed to, but it’s really not as severe
as I had thought. Even on the D800 resolution is as high, or higher, at
f/16 than it was at f/2.8. At f/11 the resolution is as good, or
better, than at f/4. And at both f/11 and f/16 resolution is clearly
higher than it was wide open. Perhaps the diffraction monster’s teeth
AREN'T as long and wicked as I thought."
A closely related topic is using R-L deconvolution on diffraction
softened images:
Recall a previous thread on this
http://lists.tako.de/Olympus-OM/2013-02/msg01884.html
Note again the fairly hard frequency cut-off on the diffraction
softened image.
Now look at link at post 66:
http://www.luminous-landscape.com/forum/index.php?topic=45038.60
Yikes, R-L deconvolution didn't do half bad ! Admittingly he used a
perfect PSF but still much of the compromised image data should have
been gone and what is there is ditributed over more energies requiring
much more intensive processing at diminishing returns to recover.
Uh, oh, looks like Dr. Diffraction's protege needs to make at least a
140 deg turn.
Take a quick look this interesitng link too--see towards the end. I
fancied myself analogous to the "Able-minded engineer" but ended up
getting a swift kick too as the hypthesis of poor results with R-L
deconvoltuion on diffraction softened images was not confirmed
experimentally.
Pin hole optimization:
http://www.biox.kth.se/kjellinternet/Pinhole.pdf
Notice the image that looked better had less spatial resolution but
better contrast.
What gives? Deconvolution sharpening does work OK to improve
images--even blind R-L does work to some degree? As in the pin-hole
example, I neglected to consider that in diffraction softend images
deconvolution sharpening can (with non-determinate PSF's) do increase
detail CONTRAST, though you can't really increase the maximum detail
frequency. It gets further confusing in that unfortunately the concept
of resolution has to be very tightly coupled to "contrast", and often
you use MTF50 contrast to get a "resolution" number. The point of real
detail extinction is significantly higher than that.
My head hurts now (hope yours doesn't )and time to go home. Sorry to
have mislead some.
Moral of the story: Don't sweat going past the diffraction limited
aperture too much if required. Expect some improvment using Focus
Magic on diffraction softened images .
Chastened but corrected the error, Dr. Diffraction protege, Mike
--
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