08-09-2014, 03:05 PM
Well, two things about this. First of all, Photozone uses sharpening of the test files before measuring MTF, which tends to lose part of the diffraction impact (sharp parts get sharpened less than unsharp parts). So, not the right source to look for the exact diffraction impact.
And then, the Pentax Q has a 12mp senosr, of I am not mistaken, at a 4:3 aspect ratio. The graph goes to 1900. When we look at the graph of a 12mp MFT lens test, we notice that the graph goes to 2550.
My guess is that the lens' unsharpness "wide open" still it catching up to the diffraction softness at f2.8 to f4, and we see a massive drop at f5.6 because when softness becomes too big the sharpening from PZ has a lesser effect.
A better source to see diffraction impact is lenstip, but the hsve not tested any Pentax Q lens as far as I know.
Thanks for the input. One interesting thing is that the (higher-end) Q lenses have a built-in 2-stop ND filter (activated via the user) to help keep them in their better apertures.
For the Q7 (and presumably Q-S1), the sensor apparently has no AA filter compared to the original Q.
PZ is one of the only sites to have done any serious reviews of the Q lenses.