So, I have decided to invest in one of these. Canon 50mm f/1.8 http://www.bhphotovideo.com/c/product/12142-USA/Canon_2514A002_Normal_EF_50mm_f_1_8.html Canon 50mm f/1.4 USM http://www.bhphotovideo.com/bnh/controller/home?O=cart&A=details&Q=&sku=12140&is=USA See, my original plan was to go with the 1.8 after it caught my eye; it's a real cheap lens with good ratings, and something that I'd get a load of use out of. But now I have discovered the 1.4, which costs almost 300 bucks and has USM. Now... who can tell me how big of a difference there is between the two? Obviously there is a price difference, but is that simply due to the USM and extra .4 to min aperture? Is there a noticeable difference in quality? Or would I get a bigger bang for my buck if I bought the 1.8 for only $75? And how is the autofocus on the 1.8? Your thoughts on this matter are appreciated.