For anyone interested this may catch one up if they have missed some of the hubbub on the topic of this lens. It is the one review site that I both enjoy (for the lack of hype and worship) and respect (for the uniformity and scientific basis applied) when it comes to reviews on equiptment.
http://www.photozone.de/8Reviews/lenses/canon_50_12/index.htm
I personally think that most of the problem is that many of the digital masses in canon land believe firmly that an "L" on the box and a red stripe on the rim means for certain that the lens is the work of the gods. It then confuses them or makes them very bitter to find that at 400 percent magnification on their thirty inch screens it is apparent that even these lenses fall under less godly realities.
Was it not once plainly understood that no matter how much one paid for speed on the ridiculous end of extreme apertures that there were tradeoffs?
I've seen this with several lenses when I was with canon. The most telling was the mythical 85 f 1.2. Sorry (and I had two copies in my time) but except under 1.8 the images were indistinguishable from the affordable 85 f1.8. Now, if you want to get a bunch of canon shooters stirred up like hornets ... try saying that out loud. Most of the time a very fast lens is not as sharp as a slower lens. That is just the way it is in the world of trade-offs I believe.
My 85 f1.2 was almost useless to me wide open unless I was on a tripod and focused manually. Heck, if you simply breathe while hand holding... you are out and might as well be crossing your fingers. Auto focus is also not as precise as people seem to need to believe when they spend thousands of dollars.
It all makes me want to go back to the seventies somehow.
So I believe that the 50 f1.2 is an extreme lens that is great within the limits of what can be engineered. It is not perfect (duh!) and if one goes in with the right expectations one should be satisfied. If one however reads too many posts (at other forums) about the sublime perfections of .... well, then what do you expect. The currents situation. Users, out a lot of dough, angry that the gods have failed them yet again!
So, where can I get a good manual focus prism for my underused F100?