LOL. Sorry, but you entirely misunderstood the point of my blog article, which had to do with the myth of diffraction as it relates to pixel size, a myth that presumes once you stop a lens down to the diffraction limited resolution of the sensor, you suddenly experience worse IQ than a sensor with larger pixels (yes, many photographers actually DO believe that). That's a different issue, though.
Smaller pixels won't automatically make the result worse, except if their small size means relatively more space is dedicated to non light gathering circuitry. But the claims I saw in that blog go further: "That means softening caused by diffraction can fairly easily be corrected with some sharpening while post-processing.". It then goes on to show that F/22 and sharpening yields the same result as F/8 here
, although even with this sample image the extra noise from F/22 and sharpening is quite obvious.
And the reason for this extra noise is simple to explain: the diffraction limited lens acts as a low pass filter, which unfortunately does not low pass filter sensor noise at the same time. Which means you lower the signal to noise ratio for higher image frequencies. Once you boost the higher frequencies, you also boost high frequency noise components, and that's what you see in that sample image.
As for sharpening, it mitigates the impact of diffraction, it does not eliminate the effects of diffraction entirely, or make lenses behave purely geometrically. Sharpening an f/22 image does not make it diffraction limited f/2 performance. There are also limits as to how far sharpening takes you the farther you stop down...sharpening an f/32 or f/45 or f/64 is certainly not going to reduce the impact of diffraction enough to produce geometric results. It does, however reduce the muddiness of diffraction blurring that affects the f/16+ image to an acceptable level. But that's all post-processing. Lenses behave as lenses behave. Anything you do in post does not actually change the behavior of the lens.
The diameter of an Airy Disk
is measured between its first minima, so yes, some extra pixel resolution below this diameter can be helpful, but after you put more than three pixels in each dimension you will barely gain extra information from higher pixel density. As you stated it: F/16 will be ok on full frame, but F/32 will bring visible loss of detail. The whole "myth of diffraction" boils down to "diffraction hurts, but later than many believe" and is therefore no myth at all, although Sigma evidently wants us believe so