Canon EOS-1Ds Mark III with ZEISS MAKRO PLANAR F2.0 50MM Sample Photo 501262 By magiclight

Yes, I agree. Stopping down fast primes a stop or two is the norm. The 50 Macro Planner is quite good in that respect probably due to being a slower lens design.

For astrophotography with DSLRs the problem for me is the lack of 'red' which is filtered out by the IR filter. Canon have a partial solution to this with their D60a. Of course serious astrophotographers use dedicated monochrome astro CCD cameras and filters.

I have a permanently mounted telescope on a large equatorial mount and living down here dont really have the light pollution issues. Plenty of cloud though.

With photography it's always a balance between factors -I am thinking of getting an equatorial mount to increase my exposure times without the "trail" effect. Currently the D800e body I use is for astrophotography is right at the color resolving limits of technology with 20-30 second exposures, at 1.4- 2.8 using ISO 1600. For the record the coma in your shot is minimal compared to the big prime Nikkors I have used. When wide open my 50mm 1.2 Nikkor rendered nearly every bright star with rings like Saturn - so ultimately you really need to stop most lens down and resort to longer exposures using an equatorial but then you run the risk of additional atmospheric effects and light pollution blowing the dark sky out. I am located at 45 degrees NORTH latitude!

Dunedin, NZ - 46 South.

Yes stopping down would improve the coma but of course increase the exposure.