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This lens will give you a half-stop above the f1.8 version, as well as a metal mount, somewhat more solid construction, full-time manual focusing, and a distance scale. The color and sharpness are excellent.

The lens is somewhat soft wide open, though you do get the use of f1.4, which will get you shots you might otherwise miss. It does well at f2, but needs to be stopped down a minimum of two stops (to f2.8) before its true sharpness is revealed. By f4-5.6 it's blindingly sharp, enough to serve as a measure for all other lenses.

This lens does not use a true USM ring motor, instead using a slightly noisier, slower, and less accurate micro motor with a full-time manual clutch. People with 10Ds (such as myself) have reported focus problems, and mine seems to miss focus under certain conditions more often than my more solidly constructed lenses. Apparently, 1-series cameras with superior focus systems work much more pleasingly with the 50/1.4.

Despite these issues, the 50/1.4 is an excellent lens. On a camera with a 1.6x crop factor (10D, D60), this makes an excellent portrait lens. One just needs to keep these quirks in mind.

Excellent piece of glass, does a great job blurring backgrounds and delivers sharp and crisp images. A must have for any decent portrait photographer.