I believe they are pretty close to the same as far as image quality. The usm will focus faster though..

I am not absolutely positive though....http://www.flickr.com/photos/djmsmc/..

Even though you are a beginner, you might have better luck posting in the proper forum: http://forums.dpreview.com/forums/forum.asp?forum=1029.

While a cheap lens will give cheap results, did you actually print-out any of your pictures? Too many people "pixel-peep" and look at their photo's under highly magnified conditions. If you were to sharpen the image (either in-camera or PP), you might find the print acceptable..

As to your specific question, yes a USM lens contains a small motor within the lens that quickly focuses the lens based upon electrical impulses from the camera. A standard non-USM lens focuses by mechanically connecting a long rod from a small motor in the camera all the way to the focusing lens. USM lenses also usually use higher-grade opticsWarm regards,DOF..

USM lenses focus faster than non-USM lenses. Main difference between the two..

As for the "hazy" photos, there are a lot of things that can cause that, besides an inexpensive lens. You can improve hazy or low contrast shots with software, and have a prefectly good shot. even something simple and free, like Picassa from Google, can make a big improvement in a lot of cases..

The Sigma is usually regarded as a decent lens for the price..

Crime Scene PhotographyA small gallery of personal work: http://picasaweb.google.com/PID885..

For a longer lens you want to check this out-.

Http://www.sigmaphoto.com/...s/lenses_all_details.asp?id=3303&navigator=3.

Available at tristate.com.

For the money it is supposed to be pretty good. though if you have the money canon lenses will beat it, but not at that price...

Canon EOS lenses all have the motor in the lens; some other makes have a mechannical connection from the camera body to the lens..

The Canon USM lens will focus faster and more quietly than the non-USM. The optical quality should be the same.Bertie..