<p>The bower adaptor on the EOS SLR has a lens to correct the registration issue (FD is shorter than EOS). This adaptor (and all its ilk) is very bad in general, and absolutely unusable with fast lenses.<br>
Try the same lens on a Sony A7 with a good adapter and there is no such problem. Not to say that every FD glass is perfect on digital, but some a real good. My 2/24 is superb, so are the 1.2/55 Asph and the 1.2/85L, the 80-200L is outstanding, etc.<br>
Some feel better on digital, for example the 2.8/200IF looks better than on film, and some are less convincing, like my 2/28. Go figure!</p>