Aperture matters some in imaging, but a lot less than it does for visual.
That's a great point. Op should not really worry about f number. Just decide what focal length they are interested in, and find a scope/lens that fills the bill.
Since it is for imaging, just take a longer exposure if you aren't getting enough photons. A bigger aperture means shorter exposures and more detail.
And if you do decide you need 400mm at f/2... well, see my profile picture.
Edited by MikeMiller, 12 January 2021 - 12:28 PM.