If you need a fast prime & don't have much $$$$ look at this

This is a 50mm canon EF mount lens when used on a 35mm film body, when this lens is used on the Digital Rebel or the 10D/20D the magnification is increased by 1.6 making it more like a 80mm lens because the DIGIC processor chip in the canon digitals is smaller than a 35mm frame. This is a standard EF lens, not EF-S and is not "full-time manual focus." Everyone should own at least one or two prime (not zoom) lenses, they are generally sharper and faster than an equivalent zoom lens. A 50mm and then something like a 100-135mm are a good pair of prime lenses for most of us. The 17-55 EF-S USM zoom that comes with my rebel is a great lens but it's a slow lens at F4-5.6; too slow to shoot available light in a gymnasium.

When you first look at this lens all you can think is "cheap," it's all made of plastic and very light. The lens has the normal AF/MF switch on the side and that's about it. As always, when buying a new lens the first thing you should do is put a UV or haze 1B filter over it to protect the lens element from dirt and damage.

I purchased this lens because I wanted to try to shoot karate demos inside a gym with available light only. I have the digital rebel (not the XT) and if I boost the ISO to 1600 I can keep the shutter speed up to 1/125 which is generally fast enough to catch action. Of course, on the XT, that high of an ISO is pretty grainy so post processing with a noise reduction package such as Noise Ninja is necessary to put the graininess back down to acceptable levels.

For the price of this lens, it's a good consumer level lens. The f1.4L version of this lens goes for over a thousand dollars--way out of my budget unfortunately.

This lens does not have the more reliable (and faster) ring USM motor, because of that fact it's necessary to pay more attention to your handling of this lens. It's recommended to leave the switch in manual focus mode when taking the lens on and off the camera and before you put the lens in the bag. This procedure is necessary because too much twisting done to that front focus ring when the lens is in AF mode can damage the lens internally so that the Auto focus mechanism no longer works.

Using it:
I used this lens for the first time a few days ago to shoot a karate test. I noticed that the lens has a noticeably harder time focusing when shooting vertically than when shooting horizontally. At times I was tempted to switch into manual mode because on fast moving subjects the focus just seemed to be all over the place sometimes. I have not noticed this issue with other EF lenses I own on my camera but I suppose it could be a camera issue as well.

The trade off for large aperatures is always depth of field. I have blown up one image to 8X10 and while acceptable, I found the faces a bit soft when the lens was focusing on the people's bodies. (1600 ISO wasn't helping either I'm sure). Most posts I've read about these lenses say the sharpness increases a lot at F2 which is still a fairly fast lens.

Until I can afford L series canon glass this lens is very acceptable for what I'm using it for. Because of the magnification factor on the digital bodies, you'll need something wider angle for subjects closer to you than about 15 feet.