Problems with Canon FD manual lenses.
Canon FD lenses are manual-focus only lenses which Canon sold in the years before switching over to the autofocus EF system. Many, particularly those made in the late 70s and early 80s, offer excellent optical quality, have smoothly-operating metal barrels and are available quite inexpensively on the used market. So the obvious thought comes to mind - can such lenses be attached to EOS cameras?
Unfortunately the lens mounts used by the two systems are completely incompatible. FD lens mounts are smaller in diameter, have a different lens register from EF lenses, rely on mechanical levers to control lens aperture, are of a breech-lock design (rotating pressure ring) and never contain autofocus motors.* EF lens mounts are larger in diameter, are of a bayonet mount design (put lens into camera and rotate partway to lock), support electronic control of the lens aperture and the lenses usually contain autofocus motors.
So. When it comes to adapting FD lenses to EOS cameras the key difference here is the lens register incompatibility. Adapters for Canon FD-mount lenses, including the two adapter models that Canon themselves sold at one point, must deal with this incompatibility somehow. Either they contain optics (glass lens elements) to compensate for the register difference and retain infinity focus or else they don’t contain optics and don’t retain infinity focus. There’s no way around this.
Canon’s optic-containing FD-lens-on-EOS-body adapters were basically small teleconverters (1.26x) and only worked properly with a number of their longer telephoto lenses - effectively transforming them into longer slower lenses - you lost 2/3 stop. The full official list of compatible lenses is:
FD 200mm 1.8 L
FD 200mm 2.8 RF
FD 300mm 2.8 L
FD 300mm 4
FD 300mm 4 L
FD 400mm 2.8 L
FD 400mm 4.5
FD 500mm 4.5 L
FD 600mm 4.5
FD 800mm 5.6 L
FD 50-300mm 4.5 L
FD 85-300mm 4.5
FD 150-600mm 5.6 L
The adapters can’t be used on other lenses because they have large protruding front elements which physically interfere (collide) with the rear lens element on other FD lenses. They were known as the “Canon Lens Converter FD-EOS” and were not sold to the public - only accredited professional photographers could acquire them through Canon Professional Services. They were apparently intended to help pro photographers who had a big investment in huge Canon FD telephoto lenses make the transition to the EOS system. These adapters are thus quite rare, specialized and hard to find today. When they appear on auction sites they tend to have rather high winning bids.
Third parties have made similar glass-containing adapters, but by contrast their optics are usually poor and thus image quality tends to be generally low.
Canon and others also made FD lens to EOS body adapters which do not contain optics, but as noted above, you lose infinity focus and so such simple metal ring adapters are really only useful for closeup applications. In fact, the Canon model (which was sold to the general public) was marketed under the name “Macro Lens Mount Converter FD-EOS”. There’s also a more subtle metering isue with this sort of adapter - see the potential problem section below. If you’re interested in this approach you could always cobble yourself together an adapter using old body caps and other parts.
But in short I don’t think that adapting a Canon FD lens to an EOS camera is worth the trouble for most situations. If you have a really expensive FD lens already I’d probably be more inclined to use it with an FD-compatible body such as a nice used T90 or A1, unless you really need some unusual function supplied by EOS bodies. You might want to do macro photography with your digital EOS camera using old FD lenses, for example.
Ironically enough, EOS cameras usually work better with non-Canon manual-focus lenses than with Canon ones. A shame, because Canon did build some very nice FD lenses years ago, many of which are available quite cheaply these days because the FD system was effectively orphaned by the introduction of EOS.
* Yes, it is true that Canon developed three “AC” series lenses which were basically FD mount lenses with autofocus motors built in. However, these lenses worked only with the Canon T80 camera and were essentially an evolutionary dead-end. So it’s not entirely inaccurate to say that all actual FD mount lenses are manual focus only.
FROM:
http://photonotes.org/articles/eos-manual-lenses/
... I just got my Canon XT today, SO CLEAN!! 
I love its clarity and definition. I used to have a Sony DSC-F707 5mp so the step up to SLR is phenom. I have a Canon A-1 35mm film camera that I got from my father so I have done SLR photography before. With it came a gorgeous 80-200mm tele that he was hoping I could use on my XT. It nearly broke his heart when it didnt mate up.:o It is an FD lens with that kind of end so I am not sure but is there any kind of adaptor that will mate this to my XT which is of course EF-S?? I know that the Auto Focus is gone but with tele you wanna do it manually anyway... but yea any help would be appreciated. Thanks so much especially for my dads sake...
