Better focussing for astrophotography

I've started using my Digital Rebel for astrophotography (star shots through my telescope). Focussing is extremely tough -- the standard-issue viewfinder screen is 'way too dim for use in extremely low light. I note that several aftermarket brighter screens are available. Has anyone had any experience with fixing this problem? Advice welcome.

One option is the Angle-Finder-C, which magnifies the image of the viewfinder either 1.5x or 2.5x (selectable).

http://www.bhphotovide​o.com …EG&addedTroughT​ype=search

Thanks for the suggestion. Does it actually brighten the image?

It doesn't really brighten it but it certainly makes one hell of a difference. By magnifying a portion by 2.5 you get a great idea of the focus. I used to use it with my 400mm + 1.4 TC on a 20D, and this combo won't autofocus, so the Angle-Finder allowed me to manually focus very accurately.

Thinking about brightening, though, I would check with someone who's done astrophotography. It's the only thing that I can think of but there could easily be something else.

Diffraction focusing is the way to go (if you have a reflector-style telescope (as opposed to a refractor)). Here's a good link that discusses various methods:

http://www.possumobser​vatory.co.nz …hy_camp_2005-focusing.htm

Thanks, all, for the excellent suggestions. The linked article, especially, was excellent.