>>2881741Ill try to explain this concept a bit:
The lens will only get so much detail, so you probably wont run into this. Accurate focus at infinity is so you NEED LiveView or a camera with the equivalent. If the image is not in focus, you are fucked because post processing wont help much
If you go to a telescope with a long focal length, this is important. Telescope optics are MUCH sharper than typical lenses. My 8" Maksutov can see details around 0.8 arcsec across. Jupiter rather than being a dim ball of mottled light is resolved into a gorgeous banded sphere and the moons have actual surface details visible
You are trying to focus details onto small regions of pixels, Too few and the details get lost, too many and you dont capture as much as you'd like
ProTip: Ive done astro with film cameras like the Contax 159MM, a 167 MT and an RTS III, a Nikon FM 2T a Hasselblad using various optics like an Zeiss 85 1.2, a Zeiss 200mm f2 and a Zeiss 350mm f/4 and my Nikkor 300 f/2. That last two lenses needs a telescope mount as I took photos of the Pleiades from a dark location, as well as Leo I (a faint dwarf galaxy 1/3 of a degree away from Regulus making it VERY hard to see or photograph
I now use a Canon 7D but hope to migrate to a FF once they get a decent one 4K video (why I want 10 gig video clips is beyond me)
