Rebel XT vs 717 Low Light No Flash

Hello. I recently purchased a 350D Rebel XT. It came with a Canon 18-55 lens. I purchased an inexpensive Quantaray 70-300 lens. I shoot alot of projects at school where there are performances on stage. I want to take the best pictures without a flash. There is not much stage lighting. I can't find a balance between pictures being bright enough and not blurry.

I also owna Sony DSC F-717 which I have used succesfully for years on Automatic with no flash. Most of the time the action, on auto, was frozen enough and the light was good.

How do I get the sharpest pictures with no flash in a (sort of) low light situation on stage?

Right now I depend on the 717 because I can't get the right combo with the Rebel XT. I knmow the Rebel is better. What Am I doing wrong?

Joe

More info is needed.
What ISO setting are you using? Are you using the same focal length with both cameras? Tripod?
Maybe you could post a shot from each and the exif data from it so we could see all the settings you are using and the choices the camera is using in auto.

The sony lense is a f2 - f2.4, while the canon is a f3.5 - f5.6 (i don't know the quantaray), that means if you shoot at tele, a difference of 2 f-stops.
To compensate, the canon will need to use a shutter speed 4 times slower than the sony.
Try to boost the ISO, or buy a brighter lens (the 50mm f1.8 is a very good lens, and also a cheap one, but won't be useful if you are far from the scene, it's also a fixed lens, no zoom here).

Norfindel-
Stage photography is really, really tough. It sounds like the Sony is built to work really well for it. But you're right about the Canon being better. Once you get it figured out, it will crush the Sony. The first thing you should do is shoot at a high ISO setting. Do you know what ISO you were using on the Sony? Whatever it was, set your Canon two stops faster on the ISO. That will effectively make up for the slower aperture on your Canon lens. And the Canon will have so much less noise that the image quality should still crush the Sony - even at a higher ISO.

If you do a lot of theater photography, you should consider buying another lens. I'd recommend either the Canon 70-200 f/2.8L IS, which costs a fortune, or the Canon 200mm f/2.8 prime. If this is a regular thing for you, and you want the best quality, then it will be worth the investment.