When the Diffraction Limit is Reached..

First see the Physics formulae for the calculation:-

http://egami.blog.so-net.ne.jp/2011-07-11

After all, the following is obtained for the Diffraction Limits, against different F-numbers (for 550nm Green light):-

F-number [f/]	Resolution [μm]
1.0	0.67
1.4	0.94
2.0	1.34
2.8	1.88
4.0	2.38
5.6	3.76
8.0	5.37
11	7.38
16	10.74
22	14.76
32	21.47

So, just say that the Diffraction Limit at f/2.8 is in 1.88um, which means that the pixel pitch size of the sensor have to be larger than that limit in order to avoid resolution loss owing to diffraction. Now, let's look back at the pixel pitch size of the Pentax Q sensor, which is in 1.55um only, that means that a faster lens with a larger aperture has to be used. In this case, a f/2.0 lens could just make it.

Btw, with that small sensor size and hence pixel pitch, what miracle should we expect? Will it work against the Law of Physics? And, should the Q user stop down the lens when shooting outdoor under brighter environment? But then the resolution will be decreased and Image Quality suffers.. And most importantly, we all knew that optics are not in optimal performance when used near wide opened. Besides, how about when the "02" kit zoom is used? In fact, it is just too slow and has gone beyond the diffraction limit by one to 2.5 f-stops already even when it is used wide opened! :-o


Related:-

Comparison of Sensor Specifications

When the Sensor Outresolves the Lens.. (How Meaningful is a 24MP APS-C Sensor?)