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Hi,
In regards to focal length...you mention 1stly that you would like to image DSO’s...A short focal length will be able to fit most DSO’s in its field of view, where as a longer focal length will only see part of a large DSO, due to its narrow field of view.
Another reason to START with a shorter focal length apart from imaging more with it, is also the ease of tracking when compared to a longer focal length. Have you even tried to track Jupiter with a higher magnification than what was regarded as useful? You have to track them damn thing every half second...This will for sure pose a new comer problems with exposure issues.
Achromatic Vs ED...if you just want to use a cheap Achromatic refractor, you will end up spending more in the long run on all sorts of filters & other accessories to combat chromatic aberration and false colour ect... The very first thing I noticed with the little 80ED I bought was when looking at Venus I could see it without all the glare and excessive brightness that plagues my Dob and previous cheap refractors...when you combine these negative effects with a camera, you will end up with much worse when capturing the image.
Honestly...I really don’t know that much...but am slowly learning more...By the sounds of thing, you actually remind me of myself when I first started here. The best advice I can give is to learn more about how all the equipment works, learn more about the basics of Astronomy and how light itself works...Grab a new book on the subject...research on Google & ect..
Why a refractor full stop?...I think the other major benefits of why so many are using the ED80 refractor is it’s small and reasonably light which gives more choice over the importance of Mount selection...The colour correction of the ED glass itself is something that wins over a reflector as well (please correct me if I am wrong)...I also believe many will say that a higher resolution or shaper contrast can be reached with a refractor than that of a reflector as well although I am sure many may disagree with that coment.
I hope some of this helps
Dave
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