A Much Dimmer and Higher Comet (Patreon)

The Comet C/2023 A3 Tsuchinshan-Atlas is now quite a bit dimmer, even without interference from the moon. My exposures last night (Oct 19) were at least 8 times longer (3+ stops) than they were a week ago.

Your starting exposures: A few days you could have gotten by with a stack of short exposures. Now you'll need to track and stack. I recommend starting with a 30 to 60-sec tracked exposure, at f/2.8 or f/4, with an ISO of 400 to 800.

Smaller, with a shorter tail: As the comet travels further from the Sun and our Earth, it is becoming much smaller, and its tail appears to become shorter at this angle from us. If you want to include a foreground land feature with the comet, a 70 to 100mm lens will still work; however, if you want a bolder comet, you'll need to go with at least a 135 to 400mm lens.

Much higher in the sky: A week ago, the comet was half way between Venus and Arcturus, and low to the horizon. Now, it is almost directly above Venus, and very high in the sky at about an hour after sunset — it took me a few minutes to find it last night!

If you wish to align a foreground feature with the comet, you'll need to wait at least 1.5 hours or more after sunset for the comet to move closer to the horizon — just keep in mind that the moon will be coming up about two hours after sunset tonight (although that won't happen until about 3 hours after sunset on the 21st).

Comet and the Milky Way: With the comet moving further to the south (and the lack of Moon interference), you can now capture the comet AND a vertical Milky Way (in the SW, just to the left of the comet) with a 50mm lens (or wider), albeit the comet is a little small! Give this a try! [This information is for those in the Northern Hemisphere.]