Quote Originally Posted by f/16 View Post
A long time ago when I had an AE-1, my 50 1.4 had a scratch about 3mm long on the rear element. The lens flared like crazy. I don't know how bad flare was before the scratch, but I doubt it could be that bad. So I assume the scratch caused it and have since shyed away from lenses that have blemishes on the glass.
It's of course worse on the rear vs the front but permanent markers can be used to diminish the effect of light scattering. Try a few searches.