When Canon introduced their new EOS line of autofocus cameras in 1988 they did something that no other manufacturer had done. They totally abandoned their previous lenses. The FD mount lenses used on their manual focus cameras simply would not fit on the new EOS cameras at all. Not only was the mount coupling different, but the "flange to focal plane" distance was longer (44mm vs 42mm), so even if an adapter was made which allowed an FD lens to mechanically couple to the EOS mount, the lens wouldn't focus to infinity. To allow the lens to focus to infinity, the flange of the FD lens would have to be 2mm inside the EOS body.
Needless to say this angered many Canon users at the time. Canon did make a small concession to the users of some of their more expensive "L" series telephoto lenses (and a few non "L" telephotos) by making a 4-element optical adapter which acted as a low power multiplier (1.26x). This was intended to ease the transition from FD to EOS for their professional user base. The price at the time was around $250, but they didn't make them for long and they didn't make many, so today they sell used for prices as high as $1000
Here's a copy of an illustration of the adapter from the original Canon instruction sheet:
As you can see the adapter has a protruding front element (similar to the current Canon TCs), which meant it would only couple with lenses which could accommodate this protrusion and these lenses are listed below:
If you couldn't find or couldn't afford the original Canon adapter, or you wanted something for their shorter lenses which couldn't couple to the Canon adapter, a number of generic adapters have been available for some time now. Priced at under $50 they're typically not really well constructed and the optics usually leave a lot to be desired.
NOTE: - As of 2015 it looks like the ELEFOTO FD to EOS adapter is no longer available in the US. See more below about ELEPHOTO in Japan.
A new adapter has appeared in the market, made by ELEFOTO in Japan. It claims to be higher quality than the $30 generic models and it does cost a little more (around $125). According to the manufacturer it's a 2-element design using coated optical glass and offering better optical performance. In addition the optical elements can be removed, making the adapter useful for macro work. Without the optics infinity focus is lost, but for macro work that is no problem and it simply acts as a short extension tube.
While Elephoto don't have a list of specific lenses which this adapter has been tested with, it should fit most FD mount lenses since, unlike the Canon adapter, there is no protruding front element. One exception seems to be the FD 50/1.8 (which fits but won't focus to infinity due to a mechanical obstruction, see below) and it's possible there may be other lenses with similar issues. On their website Elephoto say "...Optimum focal length:35mm/24mm FD; 75-210mm & 35-105mm FD; 200mm - 600mm FD lens..."
ELEPHOTO was kind enough to make a sample available to me for testing, and here are the results of that testing.
First a little about the methodology. With a Canon FD mount lens it's hard to compare results with and without the adapter since FD lenses can't be mounted on an EOS body without an adapter! To get around this I used several Tamron Adaptall mount lenses, which would be fitted either with an EOS mount or and FD mount. Since the adapter acts as (and in fact is) a 1.47x multiplier, I also compared the results using a Tamron 1.4x TC with the EOS mount and the ELEFOTO adapter with the FD mount.
All images are 100% crops from the center of images shot with an EOS 20D DSLR. The "test target" was the back of a lawn chair! Actually not a bad target since it contains a lot of both high and low contrast fine detail. Below is a typical full frame (20D) shot.
All focusing was done manually by observing the viewfinder image using a 2.5x eyepiece magnifier. From previous testing I know that the focusing via the viewfinder screen in this particular camera is very accurate.
Quite clearly the results are f1.8 are unacceptable. Very low contrast, soft images. To be fair, ELEPHOTO say that the adapter works best at f5.6 to f8, but it's still a bit disappointing that performance is so poor at f1.8. I know from previous experience that the EOS 50/1.8 works quite well with the Tamron 1.4xTC, even wide open. Not perfect, but contrast stays pretty high. Things improve slightly at f2.8 and are acceptable by f4.
Again it's obvious that there are problems wide open. By f4 things look a lot better and the image is pretty good at f5.6 and f8. The adapter makes the 24/2.5 into a 35/3.6.
Here's a comparison of the Tamron 500mm f8 mirror lens mounted on the 20D body via the FD to EOS adapter (left) and via a Tamron 1.4x TC (right).
The images are quite similar, but the one shot with the Tamron 1.4x TC is a little sharper with a little higher contrast.
On the left is the image shot just using the telescope alone, upsized by 140% to match the scale of the other two images. In the center is the image shot using the Tamron 1.4xTC and on the right is th eimage shot using the ELEFOTO FD to EOS Adapter. All three images are pretty high quality, showing that with a good telephoto lens at f5 the adapter is capable of yielding good results.
Here I looked at a Tamron 70-200 zoom at 200mm with the ELEFOTO FD to EOS adapter and the Tamron 1.4x TC.
Again it's evident that with the lens wide open (f4) there is a significant drop in contrast. Things get quite a lot better one stop down at f5.6 and from f5.6 to f11 the adapter matches the performance of the multiplier.
Here are a set of images, also shot at 200mm, with and without the adapter. To get the same image scale I shot from a closer distance with the lens alone (lens plus EOS Adaptall mount) than with the lens plus adapter (lens plus FD adaptall mount plus FD to EOS adapter).
Again it's evident that shooting wide open at f4 with the adapter results in loss of contrast. Things get better with the lens set to f5.6 and f8, but the images aren't as good as those shot from a closer distance without the adapter. This would be expected of course since all multipliers (and the FD to EOS adapter is a multiplier) result in some loss of image quality.
Though I won't show images here, edge and corner image quality with the adapter in place (on an APS-C sensor EOS 20D) were pretty much in proportion to center image quality. The adapter didn't seem to degrade image quality at the edges to a greater extent than in the center.
The optics in the adapter are easily removed for macro work, and in fact with longer lenses the maximum focus distance isn't all that close, around 8ft for a 200mm lens with a stop at infinity focus and just over 50ft for a 500mm f8 mirror lens which allowed focus "past infinity". Mechanically the ELEFOTO adapter is excellent, well machined and nicely finished.
As an alternative to a $1000 Canon adaptor that is very hard to find and only works with long telephotos, or a cheaper adapter that doesn't work well with anything and can't be used for macro work with the optics removed, the ELEFOTO adapter at around $125 isn't a bad buy if you have a collection of unused FD lenses and you don't need to shoot at wide apertures. If you have short, fast primes and/or want to use them wide open, then I'm afraid you are out of luck. There is no adapter available at any price which will enable you to use such lenses on an EOS body and retain high quality imaging. The best application is probably with slower telephotos and telephoto zoom lenses, where the 1.47x multiplier might be welcome and you'll be shooting around f5.6 anyway (f8 with the adapter in place).
Note: ELEPHOTO state that there is slight vignetting when the FD to EOS adapter is used with full frame cameras and the Canon 500mm or 600mm lenses.
Update: 2015 You probably can't, at least not easily or in the US. The links I had for ELEFOTO seem to have gone dead. when the links worked, the price was listed there as $132 including shipping. They did list a phone number in Hollywood, CA on their old webpage (which is no longer there). I believe they were looking for a US distributor, but it appears they didn't find one. There is an ELEFOTO.JP website in Japanese, and there is an FD to EOS adapter listed for 15,700 yen (that's about $130 dollars). The whole site is in Japanese though (I use Google translate to read it), but there is an order form. I don't know if they ship to the US. Their email address is listed on that page as Eftjpnattoyahoo.Co.Jp
From time to time an Elefoto adapter might show up on eBay. If there are currently any listed they should appear in the eBay box below:
Spelling note: The name on the adapter is "ELEFOTO" and the websites listed above also use the "elefoto" spelling, however on some email I've received from the company the spelling has been ELEPHOTO. I don't know if this is deliberate or if it's some problem in translation, but if you're searching for an adapter on Google or eBay, try both spellings!
Below is a link to all the FD to EOS adapters currently available on eBay.