Originally posted by Darley Thank you, that goes a long way to answering my question! So would a modern 6MP sensor be better than a 12MP sensor and if so why don't they make them?!
Not necessarily better - because you loose resolution. But perhaps better for your purposes? You can find CCD cameras for astrophotography with modern sensors in that range - but they are costly!
For what it is worth, I just took a night scene under nominally identical conditions: ISO200, 10 seconds, Pentax DA* 200mm f/2.8 lens stopped down to f/5.6 (I say 'nominally' because no one really knows what digital ISO really is). Here is first a reduced image of the entire scene taken with my 6 MP Pentax *ist DL:
Un-cropped Pentax *ist DL image; click to see larger (1280 px wide) version.
And then for comparison 100% crops of the same scene taken with the 6MP *ist DL; 10MP K200D and 16 MP K-5:
100% crops of Pentax *ist DL, K200D and K-5 images. Click to see non-resized version (approx 1600 px wide).
These are manual focus images. All sorts of in-camera noise reduction have been disabled and there is no post-processing, just JPEG straight out of the camera.
Conclusions???