Originally posted by AndrewG NY One possible issue with older lenses, particularly telephoto, is CA/purple fringing. It can often be cleaned up somewhat in post-processing but this is an area that newer designs often do better. But I wouldn't allow that to frighten you out of trying for yourself.
I'll second that. My M 400/5.6, when tested against a back lit mule deer on snow with the sun behind her, gave me a (not so) gorgeous red outline where her dark coat was against the brightly lit snow.
On the other hand, with the same lens plus a 1.4X rear converter, I shot a pair of loons on a local lake and they turned out absolutely superbly. In today's post I received a 16x24 gallery wrap from Mpix, and the print is absolutely gorgeous! I know the red is there, but it does not show at all because of the dark water background.
Don't be afraid of a 30 year old, or 50 year old lens. Just test it, find out where it won't work properly, and use it elsewhere.