I would suggest two things. My first comment is on post-processing. It looks like you upped the contrast quite a bit. While some people like this, I personally prefer to leave something like the full moon with as much contrast as it has - not much. Granted, I'll almost always increase it, but I know from experience the moon does not actually look like that. It also looks like you may have sharpened it a tad, but I can't quite tell so I won't give my rant on the "water color moon" effect.
My second comment is that going to f/16 is unnecessary, can result in motion blur, and is a poor spot in your lens. I can't actually find your lens on
this site, which has dozens upon dozens of other lens sharpness tests, but nearly all of them are sharpest about 1 full stop down, which for the Sigma 300-800 mm lens would be at around f/8 or f/9.6. Qualitative reviews I quickly looked at seem to indicate f/8-11. Not f/16.
To put it another way, after doing astrophotography for several years, writing several guides to it including my lunar photography guide on this site, and posting on these forums for 2 years, I have NEVER found someone able to justify shooting the moon at f/16. It just doesn't make sense ... unless you can offer me a justification that I've missed.
I realize that I'm being overtly blunt and not welcoming to someone who just joined the site, but it's 1 AM and I've been trying to get a non-linear least-squares ellipse fit to give self-similar results for the last 5+ hrs. So ... good shot, I know you may be loathe to fix something that doesn't seem broken, but getting/giving feedback is the purpose of this site.
