2.8 or lower astro lens?

I just did my first stack of Andromeda - M31 over the weekend and even though the results weren't mind blowing I'm addicted I've been using an old sigma 90mm 2.8 and from time to time my 50mm 1.8 but I feel like I dont have enough reach with them. I dont have the money to buy a telescope and the expensive gear that comes with them so I want to get a prime thats anywhere from 100-200mm and 2.8 at the highest. My budget is $600 max I know its not much but is there anything out there in that range? If it doesn't have AF thats ok too, though it would be nice to have if I wanted to use it for things outside astro shots.

Thanks in advance!

Damien

$600 could get you a used Canon EF 200mm f/2.8 L USM or maybe even a used Canon EF 200mm f/2.8 L USM II. Both have fantastic optics. KEH has one for $569.

Also consider the Canon EF 100mm f/2 USM. This one is also extremely good optically.

You could also afford a used EF 100mm f/2.8 Macro USM or for even less, an EF 100mm f/2.8 Macro without usm.

The Canon EF 135mm f/2.8 Soft focus also fits in your budget. It tends to get purple fringing on bright highlights when wide open. It is a good lens once stopped down a little but it isn't in the same class as the above lenses.

have you thought about buying an www.astrotrac.com with the money instead?

Thanks for the advice! Il have a look at each lens now

@ady.space Yeah, I did. It really is tempting but I would rather another lens at the moment. I can use a lens for abit of hobby astro photography at night and also as a nice, longer prime for portraits or close up wildlife during the day. An Astrotrac is definitely on the list though. Are there any alternative brands to Astrotrac that do the same thing do you know?

You might look into old Nikkor or Takumar fully manual lenses with an adapter. You'll have to manually focus for astrophotography anyway, and some of those older lenses are comparatively inexpensive but impressively sharp. I know of several established astrophotographers who use such a setup (135mm seems a popular length) but off the top of my head I can't recall names. You ought to post this question in the astrophotography forum here.

I read that astrophotographers love the old Canon FD super tele lenses like the FD 400/2.8 and 300/2.8 because of their high image quality.
But for Canon EOS DSLR you need a mount conversion, or with the longer ones an adapter (Ed Mika) and some smaller modification on the lens internal focussing system. With luck and much time you find a beaten Canon FD 300/2.8L and this adapter or a good price.
As far as I know the FD 200/2.8 did not reach infinity with this adapters. Probabyl I should test this with my homemade thinner adapter (0mm "thickness").

I converted the FD 500mm f/8 reflex lens fairly easily using an M42 adapter as the replacement. And by "fairly easily" I mean it was a real PITA. There were no electronic connections to hassle with, so it should've gone easily, but all sorts of little hassles cropped up to make it frustrating.

I finally finished the conversion and am happy with the lens' performance, but I'm not eager to try and convert another FD lens any time soon. Mika's custom replacement mounts should make it easier, but even so, it's not child's play. If you have access to some high quality long FD glass, then it's worth it. But if you're going to go out and buy some, Nikkon, Takumar and assorted Russian manual lenses are a better bargain and much less hassle.

I do not much look for Nikon and Pentax lenses, but for me it seems that their easier usable mount result in higher prices, sometimes much higher prices. At a long tele lens it was double the cost for a manual Nikkor ED lens than Canon FD L.

I have mount converted (with infinity, working iris, most times reversible) some Canon FD lenses: 24/1.4L, 85/1.2L, 100/4, 300/2.8L, 400/2.8L, 500/4.5L, 800/5.6SSC
The mount conversion is not easy, but with Ed Mika adapter it is much easier.