My 50D works great in good light, ideal for sunny days and the studio. Like many high resolution dSLR cameras it can suffer from a little bit of noise in low light conditions. In researching image noise and resolution I came across a number of documents that try to explain the issue in great detail. A simple “in a nut shell” summary being:
Higher Resolution with the same sensor size = Higher Noise
Imagine your kitchen draw open and a hand full of marbles. If you throw the marbles into the air above the draw you’ll end up with quite a few marbles in each section. If each of these sections were pixels it would be the equivalent of exposing them to lots of photons of light. Lots of charge would be created to tell the camera what the light was like. Now if you double or quadruple the resolution, making the sections of the draw much smaller, you’ll catch fewer of the marbles in each. With marbles bouncing off the walls of the cells many may not get caught. Make the cells smaller and the ratio of wall to cell surface area grows towards the walls.
This is what’s happening with the pixel size in a lot of current dSLRs. Consumers that think just in terms of pixel count not image quality are pushing the market in the resolution direction.