I have the Canon EF 100-300mm f/4-5.6 USM which I purchased way back in 1992.
I connect it to my DREBEL and my 30D and it almost never focuses. When it does focus, it is very blurry around the edges and I really wouldn't call the center sharp as well.
Manual focus is no better.
I haven't tried it on my old 35mm camera yet.
Does anyone know about a problem similar to this?
Can it be fixed?