I wonder what the advantage of using camera lenses over telescopes is for astronomy. 6" aperture telescopes can be had pretty inexpensively.
It depends, of course, on what you're trying to photograph.
I have a very ancient Criterion RV-6 Newtonian scope (6" aperture), a screaming bargain when I bought it, still a credible telescope today. But I'll never be able to stick a camera body on it.
In my extremely limited experience if you want to do deep sky you'll want a telescope. On the other hand a telescope is totally unsuitable for "here's the Milky Way at night behind some interesting landscape" shots. (Most people here mean that when they talk about "astrophotography" but to me the term conjures up taking pictures of planets, nebulae, galaxies and the like, for which you absolutely need a telescope. I was an amateur astronomer long before I was any kind of photographer so that affects my perspective.)
On my to-do list is a more modern telescope with a EF mount I can adapt to my Canon bodies.