Not sure if this is the right thread for this...
Here is my 1st attempt at star trails. The composition is not so good since my prime objective was to first get the star trails. Shot with Canon 6D, Samyang 14mm UWA lens @ ISO1600, F/4, 20s for combined 93 shots, stacked with StarStaX. Actually had to delete ~60 shots because I did not notice the lens was frosted up. Outside temperature was approx. -1C near Daejeon, South Korea.
I pre-focused (Jupiter) in live view to achieve sharpest focus. Surprisingly at F/4.0, the sharpest focus is set at the 'infinity' mark (hard stop) which is different than what I saw on my previous tests. At F/2.8, I could not get sharpest focus because I would have to move the focus ring beyond infinity and this is of course not physically possible.
1) How could I prevent frost from forming on the lens during cold winter nights?
2) How can I get sharpest focus now at F/2.8? Should I even consider shooting at F/2.8 anymore if F/4 is ok?