Originally Posted by thegableguy
I've been in a very similar boat since I got my first telescope last July, an 8" 1200mm Dob. I've also got some pro full-frame Nikons & pro lenses, and a strong desire to combine the two.
Here's what I've learned through experimentation, chatting in various forums like these, and talking in person to people who've been doing AP for years.
Firstly, you can attach your DSLR to your Dob. All you need is a T-ring adapter; I strongly recommend a Celestron Barlow adapter - they sell them through National Geographic. It's great for planets. I've printed gorgeous high-resolution (ie 20-40MP) shots of the Moon, the Sun (with a solar filter), conjunctions of Jupiter and Venus / the Moon, and even the ISS. I'm quite proud of some of them - they're better than many I've seen for sale.
However, the Dob is simply no good for DSOs, which is where the real action is.
To mount your 8" f/6 tube you'll need a fairly huge mount, like an NEQ6. That mount has a payload of 20kg, meaning it'll hold something that heavy without damaging, but the typical rule is 50-70% of payload for AP. That means with your 11kg tube, camera, rings, finder, guider etc you'd be right at the limit of a NEQ6 (and far beyond the limit of any cheaper mount like the 14kg HEQ5).
Not only that, but I'm told a 1200mm focal length is pretty brutal for a beginner. You're much better off with a shorter focal length to begin with, like 400mm-600mm.
Your options therefore are a small Newtonian OTA, an RC astrograph or a refractor.
The Newts go down to about $400 for a new 6" f/5 (or considerably more for bigger), though you'll then need a coma corrector - essential, non-negotiable - which are around $100-200.
GOOD: cheap, large aperture (shorter exposures)
BAD: tricky to focus and collimate, need CC.
The RCs (Ritchie Chrietens) are still pretty cheap, starting around $700, but they're apparently even harder to collimate, are bigger & heavier, have far longer focal lengths (meaning guiding is essential) and don't have the advantage of the fast focal ratio. These are best left in the hands of the pros, not folks like you and I with no real idea what we're doing.
That leaves refractors. Something small but useable like an 80mm x 400mm will set you back around $4-500, and you don't need anything else beyond the simple camera adapter. They're not much good for observing but they're perfect for AP, particularly beginners.
Myself, I'll be getting a HEQ5 mount as soon as I can afford one, and will simply stick my DSLR with 200mm lens on it whilst I work out how to use a mount, and learn my way around stacking software. Once I've got that under control (and once the hobbies fund is available again) I'll decide between a fast Newtonian (8" f/4) or refractor (ED80).
Oh - and allow me to assure you that simply cranking the ISO on a pro-level camera doesn't work! My camera is pretty much noise-free at ISO 10,000 for well-exposed shots (considerably better than a 5D MkII, a camera I'm very familiar with), but it doesn't work like that when taking pictures of a black sky. The only way to get properly beautiful shots of DSOs is through stacking long low-ISO exposures, which means a good go-to mount is the absolute first stop. Otherwise you're just amplifying noise as the stacking software can't distinguish between low-level noise and very faint stars. You HAVE to use low ISOs, ie 200-400. Shortest exposures you can do is about 30 seconds; ideally you want around 2 mins, depending on what you're imaging.
Hope that helps. Let me know how you go. Keen to hear the experiences of someone else new to the game.
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