Diffraction Limit

Started Aug 28, 2013 | Discussions thread
Detail Man
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Re: Yup ...
In reply to Great Bustard, Aug 28, 2013

Great Bustard wrote:

Dr_Jon wrote:

... the point where "diffraction is going to be really start killing the sharpness" depends heavily on the display size of the photo, the viewing distance, the visual acuity of the viewer, the other sources of blur in the photo, and the QT (quality threshold) of the viewer.

When "diffraction really starts killing the sharpness", that effect (as you point out) exists in the spatial frequency response at the front-end in the lens-system (not the numerous other points along the processing path). That we look at the product of all individual "stages" is quite correct.

More pixels, all else equal, will *always* resolve more detail.
- True, although a chunk of the time it will be to so small a degree you don't care, the rest of the system needs to be in the ball-park. The number of times a friend's D800 out-resolves my 5DmkII are less than you'd think as the pixel effect gets lost in other factors. (He has consumery long lenses, for example)

Goes along with what I said above -- allow me to paraphrase for the new paragraph:

Well, the point where "it will be so small a degree you don't care" depends heavily on the display size of the photo, the viewing distance, the visual acuity of the viewer, the other sources of blur in the photo, and the QT (quality threshold) of the viewer.

Actually, an assessment of possible "detail" (in comparing lens-camera systems, here assuming a lens-system free from optical aberrations, and with zero focus-error and camera-motion) depends upon the ratio of the integrals of the composite spatial frequency (MTF) responses involving the following "front-end" parameters: Wavelength, F-Number, Optical Low-pass Filtering, Photosite aperture/shape/pitch. When that ratio of integrals closely approaches unity, "the game is over" where it comes to meaningful quantitative statements about "more" detail.

Whether or not numerous subsequent transfer-functions in the image processing-chain (may indeed) further limit spatial frequency (MTF) response in such a case then becomes essentially irrelevant (if and when "signal bandwidth" is fading into upcoming "noise-floors" of the "front-end").

... That's not to say that there aren't differences in resolution still, as well as other differences, but just that, in my opinion, they are trivial by that point.

Trivial seems an aptly descriptive term in such cases.

When people start "caring about diffraction" depends, as I said, on a host of other factors, namely the display size of the photo, the viewing distance, the visual acuity of the viewer, the other sources of blur in the photo, and the QT (quality threshold) of the viewer.

Not to mention the (even more directly relevant) "front-end" considerations surrounding the complicating (MTF) effects of lens-system optical aberrations, focus-errors, and camera-motions.

DM ...

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