This professional (L) version of the FD mount lens is optically the same as the previous (Non-L)version. Both have an Aspherical element, but this one has different aperture blades and focuses slightly closer (90 vs 95cm).
f/1.2 - 22
This amazing lens drops into meh territory after f/8, but it's not too bad otherwise. I have tried it at f/8 and f/11 in studio conditions shooting infrared and it did show some annoying issues, so I think this exemplifies the importance of such stringent testing. It has a bit of a odd dip in performance at f/2.8, but luckily this lens is razor sharp wide open, it just gets a bit more vignetting with IR than it does in colour at f/1.2, so still relatively easy to correct in post. I wouldn't recommend using it at f/22, but that would be true in colour anyway, so I can't see that bothering anyone.