For its price I cannot complain. I am not sure whether mine is a good sample or not; it suffers from a fair bit of coma at F/5.6 but it also isn't overly sharp according to Lenstip.com
Mine also has a reasonable amount of longitudinal aberration which can be seen by most of the stars having blue on their tops. The other alternative is that I need to get DXO to remove some of the barrel distortion on each sub BEFORE registering.
Alternatively I could just use it on my D700 and it should look near perfect at F/2.8. I've recently come to appreciate how many aberrations a 12mp FX sensor with high pass filter can cover up
