I am having a problem with this adapter as it does not fit my Canon FL 58mm f1.2 properly. Mad The reason is that the metal pin for controlling the aperture on the adapter ring is colliding with the back of the lens. The Canon FL lens has a slightly larger metal construction at the back which prevents the adapter from fitting correctly. The pin is too close to the back of the lens causing it to hit the metal housing.
The only way it would fit is to remove the pin from the adapter. If removed, it works but there is another problem. There is now a hole letting light in. So you have twist this a little further to cover the light leak.
Also the lens for some reason focuses past infinity for distant objects even when the lens marking is stopped at infinity.
There seem to be other types of FD adapter available which not cause this problem: