a few extras:
1. although most reports suggest that outside of the very center of the frame, and perhaps even in the center once stopped down, the 50L might actually be less sharp, granted wide-open and near center frame may matter most to 50L users and it might have richer color and contrast on a large scale perhaps, maybe it fights off PF a bit more, not sure, but I haven't heard or seen a lot of evidence that the L is really sharper and overall it sounds like it is less sharp, if anything.
2. more weight for L might be a negative for many not a plus
THE BIG ONE:
3. although he suggested that maybe the build quality is worse, it is not just a surmise based upon look and weight, the build quality is arguably the worst of any Canon lens, maybe of just about any AF lens by anyone in that it has a true design flaw of such a degree that it should have been re-called by Canon years ago as well as a more minor but also real design flaw.
A. It is the only AF lens ever made to offer a clutched non-USM FTM. Ever wonder why Canon never tried that on any other non-USM lens? Because the clutches are very prone to stick and catch and break. Virtually everyone I personally know who has had this lens has had it break, often more than once. Sometimes Canon even fixes it for free years out of warranty because I think some employees feel bad about it. And if not, they have a special flat fixed rate for it (pretty curious if it is not something that happens so often that it basically stems from a design flaw). I once saw a copy break in less than 60 seconds out of the box new. (That said if you have a copy that hasn't broken after the first few years, apparently it is likely to continue lasting, so perhaps it is possible to use the design and not have it break, but it has to be machined perfectly.)
B. It uses a very low-precision AF engine (since it produces erratic focus, prone to way under and over-shooting) AND low accuracy (since it can't be adjusted in any fine grained manner internally and tends to need adjustments at all sorts of different focal distances, which it doesn't allow for). And the AF seems to vary in quality a fair amount copy to copy, some copies, the best, had hit rates 2-3 times better than the worst (scary thing is that the hit rates of the best were quite bad, that was tested back in the 20D days though). Neither of those are good in an f/1.4 lens! That said it does slightly better on 1 and 5 series than on other bodies and on the 5D3 and 1DX, in particular, you almost begin to think you could semi-trust it at times at f/1.4.
All that said, as far the optics, I once compared it to an adapted Zeiss Contax 50mm 1.4 and I couldn't tell the difference at any aperture (some say the Zeiss EF mount versions are better than the old Contax ones though) and it seems to fair very well compared to almost any 50mm corner to corner on FF once stopped down (certainly for sharpness) although some new fancier non-double G type designs such as the sigma and so on do better at f/1.4 and those $$$ Leica 50mm I hear are better (although I've never gotten to use one myself).
I don't get why Canon didn't just replace the AF motor with ring USM ages ago, or at least just give it a higher-quality regular old micromotor AF system.
Let's see: 1 body, 7 copies of the same lens. What are the common denominators here?
