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I think these lenses are also sensitive to the flange distance. For Nikon I think the flange distance is around 44mm (check that). So you can measure how far your adapter puts the sensor plane to the back of the lens.
Also as mentioned several times many lenses do not perform well wide open especially short focal length lenses. Most need to be stopped down.
My 14-24 works fine at F2.8 on a DSLR but on my Proline 16803 with a Nikon adapter it would not work looking even worse than your sample images. I suspect again the flange distance is off. The Nikon 50mm F1.8g though was super sharp at F2.8.
You can jam a tooth pick in the little spring loaded aperture control at the back of the lens.
Now you see why lenses with aperture rings are better suited to astro work.
Also 24mm wide open is supposed to be a bit weak on the 24-70 although I must admit I did not notice it on my copy and a D800e.
Try different lenses. Zooms are usually a compromise so stick to primes unless its the Nikon 14-24 which is a super lens.
Pentax 67 lenses are quite forgiving and work up to a 16803 chip very well. They are also cheap. The 75 F4.5 and the 165mm F2.8 wide open work well.
I think you will find not many camera lenses work well wide open for astro work especially fast lenses (F1.8 or less). An eye opener really about lens performance. 50mm is a bit of a sweet spot as manufacturers seem to be able to make them high quality quite easily and most 50mm lenses I have tried worked well (Pentax 55mm 67 lens not being so good).
The best lenses I have used are:
Pentax 67 165 F2.8 - really sharp and pinpoint no chromatic aberration or very little at F2.8 - rare performance.
Pentax 67 300 F4 hard to mount as its a heavy and large lens but it works well.
Pentax 67 75mm F4.5 not quite as good as the 165 but really very good overall.
Nikon 14-24 really a DSLR lens and have not been able to mount it on CCD so far with success.
Nikon 50mm F1.8g F1.8D. Both are superb. I would go the 1.8D as it has a metal aperture ring making aperture control simple whereas the G lens has no aperture ring.
Nikon 85mm F1.8g looks good around F2.8 better at F4.
Samyang 24 F1.8 - nice at F2.8 and above.
Fuji 14mm F2.8 wow what a lens, maybe a better alternative to the Nikon 14-24 for an 8300 chipped camera as it has an aperture ring, is light and is super sharp and much cheaper. Haven't tried it on a CCD but I suspect it would be good. Shorter flange distance of around 28mm may be an issue for adapters.
Fuji 18-55 F2.8 zoom - very nice not used on a CCD though.
Contax Yashica 28-85mm - worked well at about F4.
Minolta Rokkor 28mm F2.8 - not bad a bit of chromatic aberration but has an aperture ring, is cheap and has a solid reputation as a good lens.
I am keen to try my Zeiss 55 F1.8 which is the 2nd highest rated lens on DXOMark. On a Sony A7r its sensational. Whether it performs for astro remains to be seen. Again hard to adapt to a CCD as its 27mm flange distance versus around 44 for Nikon and Canon.
Greg.
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