Why Old Lenses? Unlike fancy new lenses, old lenses always have a certain charm, a story and a personality. They also keep your wallet a lot heavier! You can have a full range of very high quality glass for the same price as a single modern lens, so long as you're willing to give up the autofocus and a few other luxuries.
The Problem. I recently purchased a Canon 5D (original) and I have tried a 28mm PK mount lens on my 5D, but the bayonet style mount interferes with the shutter and I am pretty sure is causing a lot of damage and can't take photos. Without jamming any more bayonets into the mirror, I want to know if there are any older lenses that anyone has used that successfully worked on full frame Canon DSLRs with the larger mirrors.