Originally posted by Ahab Better lenses in 50mm than the FA 50/1.4? I don't think so.
Sigma 50mm f/1.4 EX DG HSM. It's better in almost every appreciable way: Less vignetting, less CAs, sharper across the board, and it has (subjectively) slightly smoother bokeh. It also produces some very bright colors and good contrast.
The only real disadvantages are size, weight, and price. Even then, the $499 price it retails for isn't bad when you consider that it beats the more expensive DA*55 wide open. I bought my FA50 when they were dirt cheap, and being my least used prime it isn't worth it to me to upgrade. But, if I was in the market for a new 50 today, I'd probably spend the extra $150 on the sigma.