Originally posted by Fogel70 You mix two things, resolution and sensor size.
Yes I mix resolution and sensor size, since they both come into play to produce the final image quality.
---------- Post added 07-08-15 at 12:56 ----------
Originally posted by Fogel70 On small sensor camera like Pentax Q it doesn't seems like Pentax get any benefit of the smaller sensor in SR effectiveness compared to APS-C.
Good point. The SR of the Pentax Q, claim to be able to stabilize 4 stops, so, as you mean, it's not better than the claimed SR perf of the APS-C line. The reason for this is the smaller sensor of the Q has less inertia , but at the same time, Q pixels are 1.54 microns pitched. So, you've just figured out that if you change the size of pixels and sensor in roughly the same amount, the SR performance spec stay the same.
Now, if you apply this to the move from APSC to FF, to keep the same SR performance on FF, you'd have to increase the size of pixel on the full frame sensor, so that the SR can compensate for the same amount of blur (pixel relative). For example, the A7 24Mpixel FF sensor SR is also 4.5 stops, like the K-3 24Mp APSc SR perf. spec. of 4.5 stops.
I let you think about what SR perf. would be for a Pentax FF with a 24Mpixels sensor, or 36Mpixel sensor, 42Mpixels, and 50Mpixels.