Too convoluted (no pun intended) for me. But I did find it interesting
that diffraction does begin to show up about where it would be expected
(discounting the performance of individual lenses). I think the news
here is how much sophisticated digital sharpening can recover...
something that wasn't possible in the days of film.
For myself I will continue to use ordinary diffraction calculations when
shooting landscape. For the 5D the diffraction limit is about f/11. If
shooting with 24mm using hyperfocal techniques at f/11 the depth of
field ranges from less than 3 feet to infinity. Perhaps I could shoot
at f16 but for what purpose? I might gain about 9" on the near distance
at the possible expense of more difficult sharpening. Also, the 5D is
much more likely to show dust bunnies at f/16 or smaller than at f/11.
For the E-M5 f/5.6 gives about the same result at 12mm (sans dust bunnies)
Chuck Norcutt
On 5/30/2013 8:45 PM, usher99@xxxxxxx wrote:
> 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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