This is a very heavy lens. Compared to the nFD 50mm f1.2, it's at least 1/3 heavier, and physically larger. It's even bigger than the FL 55mm f1.2, but weigh about the same.
Optically, this lens reminds me of the EF 50mm f1.2L. Naturally, the EF version is much better wide open. The contrast is better on the EF, although both are pretty sharp at f1.2. With a bit of contrast adjustment in post processing, f1.2 is absolutely usable on the FD 55mm f1.2. I have read many people's reviews saying the FD 55mm f1.2 is not very usable wide open, I can only imagine their opinions were based on film, where critical focusing may not be easy to obtain. Using live-view, getting exact focus is trivia. From f1.4 on, the lens is extremely sharp. If time permits, I will do a comparison of the FL 55mm and the FD 55mm f1.2, since both have the same focal length, and same number of aperture blades. One thing I do find weird, is that the FL 55mm f1.2 can not focus to infinity with the adapter I have, but all my other FD/FL lenses seem fine.
I have been using the Minolta MD 50mm f1.2 quite a bit last week, frankly, it's not a bad lens, but when compared to the FD 55mm f1.2 S.S.C, it's just not as good. First, the bokeh on the Canon FD 55mm f1.2 is sweet, even stopped down, it's very pleasing, whereas the MD 50mm f1.2 looks terry anything past f1.2. This I believe due partly to the nice 8-blade aperture on the FD, and the MD has only 5 blades, making the out of focus highlights distracting.
The colour is also very nice on the FD over the FL version. More intense, vibrant and saturated than the FL version. If anything, I think Canon lenses produce very nice colours, which I can't say for the likes of Sigma and others.
I might attempt to convert this lens again to EOS later, but in the mean time, I will enjoy it with the G1.