Hi Bart,
Could you elaborate on that one?
Sure. Microlenses refract their part of the cone of light onto the light sensitive part of the individual sensor elements, thus creating fewer wasted photons that might fall on transistors, 'wiring' (gates, connectors), or even spill to the neighboring sensels. If the angle of incident light gets too oblique, they can no longer focus on the correct part of the sensel. For lenses with a short distance between the exit pupil and the sensor, those angles are already oblique near the corners of full frame sensors. That's why the physical arrangement of the microlenses is offset a bit in modern designs, progressively more offset (less centered) towards the corners of the sensor (no longer centered above the sensel).
With such an optimized system, decentering or shifting will mis-focus the image rays and reduce the efficiency (leading to vignetting, rippling, and other artifacts).
When gapless microlenses are used, the apparent fill-factor of the sensel is increased, which not only increases the amount of light that is utilized, but the sensor also starts behaving more like an area sampling device, instead of a point sampling device. That improves its MTF roll-off towards the Nyquist frequency, and thus also reduces aliasing. The recorded signal is more true to the input signal.
Another point:
Let's say that I want a world class lens, like the Otus 85/1.4. For me it would make some sense to have a world class sensor like the Canon 5DsR or the Sony A7rII, rather than a sensor of more limited resolution like the A7II.
With the A7rII is still see some colour aliasing artefacts even with middle of the road lenses. So it is in no way immune to aliasing. With P45+ it is more of a generic problem. One of the worst issues I have seen are rippled water surfaces. But, I would say that issues with the A7rII are almost a magnitude less than with the P45+.
Yes, the OTUS and Sigma ART lenses will create a high contrast low residual aberration input signal at wider apertures. Narrower apertures will have diffraction taking over, and that somewhat reduces the differences with lesser lenses.
The sensel pitch differences (denser sampling) of the A7rII versus the large P45+ sensel pitch will reduce the aliasing, because the Nyquist frequency of the A7rII is much higher, and there will be fewer small details that will cause aliasing, if the same focal length is used. If a shorter focal length is used, then the image magnification is reduced and there will be an increase of small detail in the input projection, maybe cancelling the benefit to some degree, but diffraction per pixel can be more (depending on aperture number used), acting a bit like an (inefficient) AA-filter.
My guess is that fill factor plays a very major role, so modern sensors with large fill factors are less prone to aliasing than older sensors with a smaller fill factor.
That's correct.
Cheers,
Bart
