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Re: [OM] 28-200mm Lenses

Subject: Re: [OM] 28-200mm Lenses
From: Moose <olymoose@xxxxxxxxx>
Date: Wed, 26 Nov 2014 15:46:53 -0800
On 11/21/2014 1:55 PM, Mike Gordon via olympus wrote:
...
responding to Moose:

for digital has allowed the niche designers to lean towards resolution, at the 
expense of contrast, as that's something
that may be corrected without loss in post?


Well I see what Ed is getting at and Moose at the same time. I think there is a definitional conflict rather than conceptual.

Very possibly so. When working with film, what our eyes perceive as 'sharpness' is some combination of actual resolution, separate from contrast and contrast itself, including acutance = edge contrast. In the digital darkroom, these become (as they always were, underneath), separate things that just happen to interact to produce the undefined quality of sharpness.

A I hope I demonstrated in my last post on the subject, ANY low contrast caused by a normal lens may be entirely recovered in post. In addition, some, often quite a bit, of resolution may be recovered by resolution. In combination, a great deal of preciously invisible detail may be "recovered". I put that in quotes because it's really taking what's there, but not visible to our eyes, and making it visible.

I was never sure how to resolve this. MTF at higher frequencies does correspond 
to resolution and lower frequencies to
"contrast." But with no contrast there is no resolution as in white lines on 
white paper.

MTF has never made all that much sense to me. Here, it seems to me to 
perpetuate the sharpness ideas of old.

With the Moose use of the terms:
Thinking of reduced global contrast with preserved finer details as in the Sigma 600 mm CAT--responds dramatically well to PP contrast enhancement.

Yup. The shot of Half Dome I just posted was shot through 8+ miles of air with that lens. The original is pretty low contrast. :-)

http://lists.tako.de/Olympus-OM/2014-11/msg00264.html

To quote myself from the post:

"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."

Recall Convolusalated Moose's excercise:

<<<< But wait! How about a little exercise? Just as theoretical, in a way, but 
the processing is real.
<http://www.moosemystic.net/Gallery/tech/DiffractionContrast/diffracted_sweep.htm>

So did he increase resolution?--effectively yes though largely altered contrast. No real new resolution data was added however as what data was there just enhanced.

From invisible to the human eye to visible.

With deconvolution (especially with a specifically designed PSF) one could 
argue resolution was indeed enhanced
though that may become a semantic arguement.

But as a matter of practice, detail that was not visible or not clear becomes visible/clearer, and it's what we see that matters. :-)

Such totally subjective measures as sharpness -- clearly a f(resolution, 
contrast, microcontrast {acutance}).

But it's how we see, and photography is for our vision, not theory or machine measurements. By that standard, contrast adjustment, edge contrast adjustment, LCE, and/or deconvolution can enhance 'sharpness', often dramatically.

The other factor not addressed, but relevant, is sampling effects. Six years ago, I wrote on Zone-10.com what I think is a pretty good piece on why some kind of edge sharpening is necessary because of the way digital capture affects edges.
---------------------------------------------
"However, I would like to make one thing clear. /Any form of digital capture/ reduces sharpness of an image /below/ that implied in the resolving power of lens and/or sensor. Although the problem is closely analogous to problems of digital music recording, and I suppose the math may be much the same, the way we experience and talk about it is different.

...

Now comes the simple thought experiment, although for those with proper windows, this is safe to do at home. Imagine a window consisting of many smaller panes. Draw the curtain on one side to a point where it covers half of a vertical row of panes. If we convert that to digital, the covered panes are black, 0, the uncovered ones are white, 255, and the half covered ones are middle grey, 127.

Immediately with no failing of any lens or processing, the transition from black to white is defined not by 2 pixels, but 3; acutance, and thus perceived sharpness, is diminished. The very process of sampling on a fixed grid reduces sharpness below what we might expect from the pitch of the sampling device.

Now, for those of you doing this at home, pull the bottom of the curtain to the side, so that it crosses the window at a diagonal. Oops, now we not only have middle grey, we have a bunch of panes partially covered to different degrees, and thus a range of different non-black or white pixels representing what is clearly a sharp line.

...

Put it all together, and the image of even a perfectly straight line dividing perfectly white and black areas gets foggy at the pixel level. So the unfortunate truth is that ALLdigitally captured images, including scanned film, require some sort of enhancement to reveal to the human eye all the details they contain."
---------------------------------------------

In theory, I suppose, that would mean that USM sharpening should be the choice for capture sharpening. In practice, the effects of lens aberrations, diffraction and capture effects are all mixed together, and I find mild generic deconvolution generally does a better job.

In Contrast to Moose

--
What if the Hokey Pokey *IS* what it's all about?
--
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