Conclusion: The Canon EF 85/1.8 USM is a very good lens. It's one of Canon's best lenses and it's certainly near or at the top of the list of Canon's best value lenses. It's far and away better in all respects than any comparably priced zoom lens, and probably arguably better than any zoom lens regardless of price.
Summary: Canon EF 85mm f/1.8 USM is one of the best medium telephoto prime lenses in Canon's arsenal. Combination of stellar performance with both APS-C and FF type cameras and affordable price, make this lens an interesting choice for general as well as portrait photography. There does seem to be some variation in quality among different samples of this lens - the difference between the two samples I tested was sufficient to turn the lens from an average to a stellar performer.
Excerpt: Originally posted 2011-02-14 on Optyczne.pl If you own a Canon 35-mm reflex camera nowadays your selection of classic portrait 85 mm lenses is really large. The list can be started by the expensive but splendid EF 85 mm f/1.2L USM II – a lens you would look for in vain in other systems. If you are not as well off to afford it you can opt for a quite old (launched in 1992) but much cheaper EF 85 mm f/1.8 USM.
Cons: noticeable longitudinal chromatic aberration,, modest accessory kit,, lack of repeatability of particular specimens.