does anyone know if there’s adaptors to fit old Canon FD lenses onto A 5D body? Or would that be like putting a pair of deore hubs into an Indy Fab?!
The trouble with the FD lenses is that they’re about the only lens that needs mounting closer to the sensor on an EOS camera than the stock lenses. This is impossible due to the mirror (especially on full frame), as the adapter has to take up some positive space. You can get two types of adapters though. The first doesn’t allow infinity focussing (this is what you lose when you mont the lens too far away – like an extension tube. It is however great for macro or closeup work.
The second type of adapter has a corrective lens in it to allow infinity focussing. But where the FD lens is presumably an L-series one (or you wouldn’t be wasting your time trying to fit one to a 5D), the quality of the adapter’s glass can be questionable to say the least, ruining the image.
Ironically, it’s much easier to fit just about any other manufacturer’s old lens to an EOS camera than it is an FD-series lens.
I’m afraid that if you go for a 5D, and certainly a 5DII, you’ll be found out on lens quality if you don’t buy very carefully. There are lots of old lenses that have the quality (pretty amazing when you compare the 6-8 MPx at best you can get out of a 35mm slide before all you’re resolving is film grain), but there are also plenty that don’t. As a rule, most of the Olympus OM-series are fine, but sometimes require a little CA correction in PP. The Tamron SP lenses are also surprisingly good, and you can find plenty of good M42-mount lenses. As said, old pro-level Nikon stuff is also good, but as these natively fit modern Nikon cameras, there’s usually a premium.
Your other option, if you need AF and full metering, is to go for the mid-range primes, which whilst not ‘L’ build quality, they certainly have the image quality in most cases.
I think in full frame, the EOS platform wins hands down in terms of bodging old lenses. Nikon can obviously use their own-brand old lenses, but due to their design, just about every other lens would require an adapter like the FD lenses do on the Canon. Olympus are your other option for being able to use lots of old lenses, but they don’t do a full frame sensor, which is a show-stopper for me.