Do you have a cupboard full of old manual Canon lenses that you want to try using with a newer autfocus EOS body? Don’t know if it will work or not? Bob Atkins has the answers:

“Clearly using a manual focus lens is inconvenient, but sometimes it can be worth it if the equivalent EOS lens is expensive, if you shoot mostly static subjects and if you don’t use the lens very often.

Most EOS bodies will give quite good exposure when using many manual focus lenses, but some lenses may need exposure compensation set on the EOS body. The only way to tell is to take some test shots and evaluate the results. Operation in manual or Exposure Priority (Av) mode is possible, but not in any program mode or in Shutter Priority (Tv).”

Website: Bob Atkins - Using Manual Focus Lenses on Canon EOS Bodies