Started 7 months ago | Discussions thread
fvdbergh2501 Contributing Member • Posts: 516
Re: Microcontrast

Joofa wrote:

Great Bustard wrote:

  1. If System A has a higher MTF-50 than System B, does that mean that it will have greater resolution at all other contrast levels? For example, will the MTF-10 and MTF-90 of System A also be greater than System B?

IMHO, some of the answers you are getting in this thread are not entirely correct in the context that you have posed the question. (For e.g., the graphs shown here, and here.). You have posed the question in the context of a picture as in digital photography. The correlation structure in a natural image restricts frequency content to a range in the (relatively) lower frequency in an image. After that it is just noise. All that arguments in the quoted threads are actually trying to find (micro) contrast in noise! Even their own graphs seem to suggest that in the relatively lower frequency region (where most of the image content lies) the MTF curve which is higher stays more or less higher.

I think you misunderstood what my post shows: the OP wanted to know if halation (taken to mean spherical aberration) affects MTF50. The MTF plot demonstrates quite clearly that:

a) The hypothetical SA-affected lens at f/1.4 only just manages to achieve a comparable MTF50 value, despite the fact that we would expect much higher MTF50 values in the absence of the simulated spherical aberration. This meets the first part of the OP's question.

b) The simulations also demonstrate that the contrast of a system suffering from spherical aberration can indeed be higher at higher frequencies, even in the case where the two systems were matched at MTF50. (second part of OP's question)

In other words, my post provided a simple counterexample to address one of the OP's questions. Nowhere did I claim that the additional contrast beyond Nyquist was a good thing; you must have missed the phrase "false detail (aliasing)" in the caption of the simulated image, or the later phrase "but in reality that is just aliased false detail".

Regardless of the obvious aliasing beyond Nyquist, the simulated system with SA (green curve in the MTF curve plot here) does indeed have better contrast at high frequencies but still below Nyquist, which is consistent with the OP's definition of microcontrast.

At no point did my post claim that I supported the OP's definition of microcontrast, or that high contrast beyond Nyquist was a good thing.

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