5d IV + sigma 35mm settings?

Am new to astro but understand the jist of shooting+pushing night images, but wondering if there are recommended settings for this setup?

Should I shoot iso 3200 and push it more or iso 6400 and noise reduce more? Seems at 35 I should definitely stay under 10s, some test shots had 6-8s as the sweet spot...

For the lens, should I go all the way to 1.4? I've heard the coma+vignetting will be worse there - but if not 1.4 where is the sweet spot? 1.8, 2, 2.8?

Thanks!

There are a couple of formulas that can be used to compute the time... but the easy method is to just divide 500 by the focal length of your lens. 500 ÷ 35 = 14.3 (you could just round that to 15 seconds). That’s the amount of time it can leave the shutter open on a stationary tripod.

If you used a tracking mount (e.g. Sky Watcher’s “Star Adventurer” or iOptron “Sky Tracker” ... both companies make a version of these that handle 5.5 lbs ... and also sell a slightly more expensive version that claims to handle up to 11 lbs of weight) on a decently solid photo tripod ... and such a setup would let you take much much longer photos (I’ve done 8 minutes with a 135mm lens and can’t detect any star elongation).

The 5D IV would probably handle ISO 3200 with extremely low noise.

You typically will a bit of coma if you shoot completely wide open. But every lens is different so I suggest you experiment with that to see what works for you and your lens. Maybe it’s f/2... maybe you’re ok with f/1.4 (hey, it’s art!). The stars will look a bit better if you can manage to stop it down slightly (you usually get a big improvement for just a tiny bit of stopping down... and then a slight improvement (not as big) if you stop it down more. That is to say... just a little stopping down wont necessarily make perfect stars, but it’ll be a huge improvement.

There are always trade-offs ... so this is about striking a balance that gets you results you enjoy.