I used an ED80 at one point like a telephoto lens and it was great. Its light and I was able to focus fast enough to image flying birds in the distance.
Those guys who spend $15G on their huge Canon and Nikon lenses are really keen. I think you get similar results with an ED80 and some scopes these big lenses can't even match although the weight and lack of autofocus could be a pain.
As far as camera settings goes. I find using autoISO on late model cameras is a good strategy. Then the exposure takes care of itself especially if it has a minimum shutter speed option.
A rig like a Fuji XE1/XM1 or Sony Nex and an ED80 would be very lightweight and easy to handle.
http://www.pbase.com/gregbradley/image/142376966
Done with a Canon 40D and a TEC110 fluorite (a bit heavy for this type of work but a superb lens and check out the creamy bokeh!). I can't see a $15G Can/Nikon matching one of Yuris fluorite triplets (it has about 1/6th the number of lenses for a start!).
Greg.