Daniel will definitely answer this in a more detailed fashion, but here's my impression:


the difference between f/1.8 and f/1.4 is not HUGE, it's reasonable, though. Both give good DOF.





Now, comparing the 2 lenses:


the 50 1.8 doesn't have USM or an 8-blade aperture. Build quality is terrible. $90


the 50 1.4 has USM, and an 8-blade aperture. Build quality is reasonable. $300


The 1.4 @1.4 has the same sharpness of the 1.8 @1.8. and so forth. Point: with the 1.4 you can get sharp results at wider apertures (Daniel?)





my 2¢: get the 1.4


brendan