Let's say we have two sensors, one twice the size (4x the area) as another, and, for the sake of simplicity, assume no AA filter. Let's say we use two lenses that each have the same resolution (lp/mm) at the same DOF (e.g. f/4 and f/8).
How will the resolution in the photos (lw/ph) compare if:
- the sensors have the same pixel count?
- the sensors have the same pixel size?
Repeat the question where the lens used on smaller sensor is twice as sharp (lp/mm) as the lens used on the larger sensor.
Do the answers depend on the contrast level at which the sharpness level is measured?
I think the answers are rather straightforward, but that the reality of today renders the answers moot.
From a practical point of view the sensors are far enough away from the resolution limitations of reasonably good lenses at reasonable apertures that the final mtf at high frequencies will depend a lot on sensor resolution. And as long as we are in that domain, more pixels will simply produce substantially higher resolution.
Even a lens lens such as the venerable low cost Canon 85mm f1.8 has resolution enough that the sensor in the 5Dsr produces ugly aliasing here at DPR. And the modern designs perform much better, and are just more limited by the sensor.
And there are no half size sensors with that kind of resolution, 20MP is the most you're getting, so any comparison at similar sensor resolutions at higher level is impossible.
Roger Cicala has produced some mtf data for m43 lenses, but not anywhere close to Nyquist for modern sensors, which is also true for the lenses catering to the 35mm sensor format, so reasonable data for comparison is thin on the ground indeed.
From a practical standpoint, while m43 lenses may actually resolve twice as well as some FF lens counterparts, they don't do twice as well as the best. (There may for instance be tolerances in manufacturing that are constant regardless of image circle.)
For example, the superb Olympus 45mm f1.2 is not quite twice the resolution of the equally superb new Canon 85mm f1.4 at corresponding apertures (2.8 vs. 5.6) . It's not terribly far off though, so designing for a smaller image circle and absolute aperture seems to bring benefits.
But the resolution advantages in lp/mm of lenses designed for smaller image circles is largely wasted if the sensors aren't available to demonstrate their pedigree. It's a bit of a mystery to me why you would produce excellent lenses and then hamstring their performance by middling sensor resolution. It would seem to weaken the case for lucrative lens sales. Nevertheless, that's where we stand today.
