Originally posted by dtmateojr Yes, diffraction kicks in at the same aperture.
there are some unsubstantiated and/or illogical claims in that link: "To fully utilise a 36Mp full frame sensor, one has to shoot at f5.6 or wider. At f5.6, a perfect lens is capable of fully utilising a 60Mp full frame sensor. At f8, around 30Mp. We therefore say, that the Nikon D800 36Mp sensor is diffraction limited at f8."
let me correct that statement... "to fully utilize *any* sensor, one has to shoot at f5.6 or wider" ...the only test results that i've seen that show higher resolution at f4 are due to lens design, not sensor size... that is proved by the fact that another lens will have a higher resolution at a f5.6 or smaller, on the same sensor.
fa35 f2 showing more resolution at f4 than at f5.6... it's not just all about the sensor:
http://www.photozone.de/pentax/123-pentax-smc-fa-35mm-f2-al-photozone-review...report?start=1
f5.6, f8, etc., are not physical sizes, like inches, and their actual measurement is dependent on focal length.
other issues there revolve around pixel size and spacing on the chip(aka pixel density), and whether or not the lens itself is diffraction limited.
look at the lensrental link i posted, 36mp a7r sensor vs. canon 21.1mp sensor, exact same lens on both, and both are full frame sensors:
canon @f4: 1045 lines
a7r @f4: 1400 lines
clearly, more pixels can equal higher resolution.