On 5/30/2013 10:35 PM, Ken Norton wrote:
> My belief, based on testing and empirical evidence is that diffraction
> blurring is not to be worried about in most cases.
"Matching experiments trumps any theoretical argument.", Scientific American,
April 2011, The Inflation Debate, by Paul
J. Steinhardt
> The common mistake
> the diffraction police make is using the calculation to assume an
> entire circle of 100% blurring. In the real world, this doesn't
> happen. It's actually a reduction in the edge contrast, not a total
> blurring of the edge contrast. In fact, in most cases, the diffraction
> blurring is masked by the AA filter or raw converter that essentially
> averages three or four pixels together.
>
> In my experience, the calculations are a full stop off, when using
> digital cameras. Diffraction blurring is much more visible on film
> than digital. In fact, I'd go as far as to say that two stops off
> might be more realistic, because the blurring is so easily corrected
> by sharpening.
That agrees with my experience. The calculations apparently say things should
start to get bad past f8 on 4/3, but f16
is fine for real world, 3D images. F22 is where the trade off between focal
plane sharpness and DOF seesaws. This is
after appropriate NR and sharpening. If you shoot lots of really flat things,
like resolution charts, you may have to
back off a stop, or not.
> Why does it respond well to some forms of sharpening? Because the blur
> disk is not 100%, but is a lessening of contrast within the zone.
The theoreticians may say whatever they want. On 4/3 images shot at any f-stop,
including f11-22, deconvolution
sharpening does, in fact, make a big difference in clarity of pixel level
detail.
> To paraphrase Moose: Put the calculator away, turn off your computer,
> grab your camera and go outside and shoot.
Then when you return, find out for yourself which apertures do what to/for your
images. Remember, all those DOF
calculations are not absolute, but originally calibrated based on averaged
human opinion. I'm not sure if the
diffraction math was ever even tested against human vision.
Back In Sync Moose
--
What if the Hokey Pokey *IS* what it's all about?
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