Conclusion: The Canon EF 50mm F1.4 USM may be based upon a 37-year old optical design, but its performance in our studio tests clearly shows that it's not giving up yet. Sure the hairs are beginning to grey a little, and Sigma's new young pretender can outmuscle it comprehensively at wider apertures, but this...
Pros: Excellent image quality when stopped down, Essentially no lateral chromatic aberration, Fast and accurate autofocus with full-time manual override
Cons: Distinctly soft and 'dreamy' at wider apertures (F1.4-F1.8), Bokeh chromatic aberration, most visible at wide apertures, Vignetting at wide apertures on full frame (essentially disappears by F2.8), Somwhat susceptible to flare
Excerpt: Canon's 50/1.4 is a bit heavier than the 50/1.8 but it gives you simultaneous AF/MF because of its USM focusing motor . It is one f-stop slower than the 50/1.0 but much lighter weight and less than one-sixth the price.
Summary: Canon EF 50mm f/1.4 USM should probably be considered the best alternative among Canon's four 50mm lenses (in terms of value for the money, overall performance and capabilities). While not as fast as its more expensive 50mm f/1.2L USM variant, this lens performs as well (if not better) pretty much...
Conclusion: The Canon EF 1.4/50 USM is undoubtedly a well-done lens. The picture quality in the frame centre and at the edges is very good at apertures above f/2.0 – you can count it among the biggest assets of this device, apart from the solid workmanship.
Cons: by f/1.4 the image is distinctly „soft”,, very high coma,, susceptibility to flares,, visible distortion on full frame,, very high vignetting on full frame.