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

Great Bustard wrote:

First, let me define the term: microcontrast is the contrast at high spatial frequencies. With that definition in place, a few questions:

  1. Does halation affect the MTF-50 measurement? If so, does the effect of halation result in greater degradation as the contrast level of the MTF measurement increases?

Others, like AiryDiscus, have already demonstrated some MTF curves that exhibit the properties you describe, i.e., two systems with very similar MTF50 values but very different contrast at higher frequencies. I can offer some simulated images generated with the MTF Mapper tools. Here is the comparison of the MTF curves:

Interestingly enough, my parameter choices appear to produce better contrast at both low- and high frequencies.

This is what the non-microcontrast lens (corresponding to the blue curve above) looks like:

Notice the total lack of detail between the "1" and the "0" marks on the trumpet

Next up, the "microcontrast" lens:

Notice the false detail (aliasing) between the "1" and the "0" marks (click to view at 100%)

For my "normal" lens, I simulated the lens stopped down to f/16. The simulated microcontrast lens was wide open at f/1.4, but with a large amount of w040 spherical aberration.

The "glow" in the image rendered with the lens with spherical aberration is not as pronounced as I had hoped, but at least these two examples demonstrate that a lens with more contrast at higher frequencies (here taken to mean beyond Nyquist) does appear to capture "more detail", but in reality that is just aliased false detail.

Just for fun, and to produce visible "glow", I ran another simulation of a system with an MTF50 of only 0.075 cycles/pixel:

Now that is a lot of spherical aberration!

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