Also. try Bakhtinov's mask
http://www.iceinspace.com.au/forum/s...ad.php?t=35676
I am using it with my 1000mm lens, it works very well. Some others claim it works with shorter lenses too, but I haven't tried, my 200mm lens (and 50mm as well) can be focussed perfectly well without B-mask.
(and focus assist and Magnifier are still useful here)