Is that why manufacturers make lenses for their cameras that exceed the Nyquist frequency? By using a low-pass filter with high-resolution lenses, the manufacturer can keep the final resolving power of the image close to the Nyquist frequency over the aperture range. Actually, the final resolving power should be below the Nyquist frequency as it is at the Nyquist frequency that aliasing is apparent. Your solution presents a problem - at which aperture should the resolving power of the lens equal the Nyquist frequency?
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Most manufacturers rightly make their lenses to have the highest MTF possible at all frequencies, but with digital it is more important to have high MTF below Nyquist than high MTF above Nyquist. Also, with digital, high MTF at lower resolution is often more important than low MTF at high resolution. It's Leitz vs. Zeiss all over again.
Alaising does not occur at Nyquist as you state, but rather above Nyquist. For further explanation of these topics, refer to this paper from Schneider. Look at figure 3; which lens would you prefer? Also, your use of resolving power without specifying contrast is incomplete. Alaising with MTF of 10% or less usually is not apparent to the eye. Point and shoot digitals do not use low pass filters, because they are not needed. The lens acts as the low pass filter, since the MTF above Nyquist is low.
[a href=\"http://www.schneider-kreuznach.com/knowhow/digfoto_e.htm]http://www.schneider-kreuznach.com/knowhow/digfoto_e.htm[/url]
You misinterpreted my comment about resolution above Nyquist. It is not currently possible to design a lens with high MTF right up to Nyquist and no response beyond Nyquist and that was not my suggested solution. Rather, the solution is a low-pass filter as we both suggested.
Alaising that produces colored Moiré is particularly bothersome, but with natural subjects without repetetive patterns, alaising may not be that apparent and the false detail that it adds may even appear to increase image detail. The ill fated Kodak full frame 35 mm style camera used no low pass filter and was noted for its sharpness.
Lens transmission can impact contrast and so influence the MTF curve.
But I am afraid we will need to disagree. Like Micheal said, it is a rather academic subject and does not really have a lot to do with the problem of taking pictures. After all, the contents of the picture are far more important than the contents of an MTF plot. As far as the quality of modern optics, there is very little to worry about. They certainly exceed the standard of diffraction limited, which was your question.
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Really? If you put a neutral density filter over your lens, does MTF suffer? What is the difference if the light is absorbed by the lens elements rather than the filter?
The subject has a lot to do with taking pictures, whether or not you go into the physics. The whole point of Michael's article was that with a lens that is diffraction limited at full aperture, stoping down degrades image quality. Unfortunately, contrary to you assertion, relatively few lenses exceed the standard of diffraction wide open, especially fast zooms.