Runnicle wrote:
Since focus peaking on Nex with e-mount and manual lenses is detecting contrast differences, would it not follow that peaking would be maximuzed on lenses with high contrast rather than just a reflection of how sharp a lens is?
Yes, peaking is measuring (micro)contrast, but high contrast at the pixel level is highly correlated with a high MTF. Thus, especially in a magnified view, the degree of peaking for the same scene imaged by one lens vs. another is a very good indicator of high resolution at high microcontrast (i.e., high sharpness).
This leads to a very controversial point I've made several times before: it is true that some lenses that have very low microcontrast can actually out-resolve ones with high microcontrast. Consider two lenses. Suppose that the (2D) energy distribution in the in-focus PSF of each is:
Which energy distribution gives higher sharpness?
Let's assume the total energy (area under each curve) is the same. Clearly, the blue curve has more energy placed within any diameter region around the center -- thus, it has higher microcontrast and would get a higher MTF 50 resolution. However, there is a much sharper point in the red curve. Thus, it is actually possible to resolve finer detail with the red lens (but at lower microcontrast until some tonal adjustment is made).
There are plenty of exceptions, but modern lenses tend to look like the blue and older ones like the red. Why? Better coatings improve contrast but looser tolerances (due to autofocus, etc.) don't give as sharp a point. Given that digital cameras linearly count photons but our sensitivity is logarithmic, I claim the red lens can reliably outresolve the blue one with good microcontrast
after a little postprocessing.
For what it's worth, the lenses that show lots of peaking at all magnifications tend to have energy distributions that look like sharper-sloped narrow peaks... which is good no matter how you think about it. Well, unless the peak is too small, and then we have to start talking about anti-aliasing filters and such. ;-)
