I've always wondered about the 50 f1.0 L... I've read that it was discontinued due to cost, but doesn't the 85L have more glass than the 50 f1.0? Is it something about the design?
from what i know about lens design, the only thing prohibiting fast telephoto lenses is size/weight/cost.
But the wider the angle, the harder it is to deisgn something fast with decent IQ, especially at the borders, and especially once you get wider than the diagonal (43mm for FF). Look at the photozone.de reviews of the 35 f/1.4 and 24 f/1.4, their centre sharpness is off the scale at f/2.8-4ish. but their border sharpness is off the other end of the scale at f/1.4.
the 85 1.2 ii is sharper than the 50 1.2, for sure, but it's not the stellar performer itself either. the 50 1.4 looks better on paper, but it's got its own problems as Neuro mentioned (in short, every lens purchase is a decision between what good you need and what bad you can put up with).
I can't find a review of the 50 1.0 on any modern site, too old and i suppose no reviewer can afford it (or noone can afford to lend it to them). the only one is from the site where wikipedia cites here
, and that was on film. If it didn't stand up to film, it definitely won't stand up to 20+ MP.
From the canon Camera Museum, it weighs 985g, only 40g less than the 85 1.2 (i or ii). so near enough to the same amount of glass. It's what they do to the glass and what it's made of that makes the cost, and i'd suppose that with all the manufacturing costs put together, plus a decent margin, it was out of reach for anyone but the most dedicated, even then you'd make more money selling to pro portrait-takers who'd rather use an 85 or 100/135mm.
i'm almost wondering, with digital and APS-C these days, if we might see a resurgence in demand for it enough for canon to release a 50mm f/1.0 II version? It makes a bit more sense taking a portrait with a 50mm lens on a crop body than a FF (but then why use a 7D to take a portrait?). and the original f/1.0 was designed in 1989, with computer design i'm sure they could beat the performance if they started fresh now...