Diffraction does not limit number of megapixels per se. It just limits the smallest size of pixel for any given wavelength and F-number.can please someone tell how the diffraction mpx limit is defined?
Due to diffraction any point source of light turns into Airy disk and sensor can't distinguish two point sources after the diameter of Airy disks is at least twice the the size of single pixel. Airy disk becomes larger as F number increases and aperture size decreases.
If we take the "41MP" IMX492 sensor as an example, it has pixel size of 2,315um and therefore diffraction will start limiting resolution after F4.
Note that resolution is limited by either aberration or diffraction whichever comes first and I seriously doubt whether even best MFT primes are up to the requirements of this sensor because it equals over 160MP FF sensor. Aberration is a collective term for all optical defects which limit what we know as lens "sharpness"
To add insult to injury, aberration reduces resolution wide open so lens has to be stepped down but in this example (41MP MFT sensor) diffraction will kick in almost instantly and leave us with, say, from F2 to F4 for maximum resolution which is really on par with the sensor pixel count (pixel size really).
This will only have impact on pixel peepers though since who would ever view 41MP MFT images in their native resolution anyway.