Is the USM lens much better than the regular Canon EF 75-300mm f/4-5.6 III Telephoto Zoom Lens?

Answer 1

The USM gives you much much faster auto focussing performance, so yes, I'd say it's much better then the non-USM version.

Answer 2

USM is lens have Ultrasonic Motor inside them, which makes them focus much quicker and silently. I think you are actually confused here, the Canon EF75-300mm f/4-5.6 III is already a USM lens, i think what you means is IS (Image Stabilizer). There are two versions of Canon EF75-300mm, one is IS which costs approx £400 and the one without Image Stabiliser costs approx £170.

I would suggest buying IS lens, you won't have to worry about blurry pictures while using such a big zoom. I own Canon EOS10D with 75-300IS lens and 17-40mm L USM (The best lens ever, crisp sharp photos). You can take a look at the photo taken using 17-40mm by clicking here: http://www.airliners.net/search/photo.search?front=yes&maxres=500&keywords=manish+wadhwani

Answer 3

I have the 75-300 IS lens, and it's definitely worth the money over the non-IS. I had a non-IS Promaster zoom, and while the shots came out good, if I was doing quick turns for tracking targets, I'd often get blurs. With the IS lens, I rarely get blurring. Also, with an IS lens, you can take shots in much lower light with a full apeture and no tripod without blurring.