I have the first digital rebel and as of lately my

when you take the lens off .. there is a mirror and the CCD array ... those can get dusty or if anyone smokes around the camera then that gets on these parts .. you can dust the mirror and CCD behind with a soft clean camel hair brush but a good cleaning should be done by a pro .. thats a "front surface mirror" .. that is, the mirror surface is not protected by glass the way mirrors normally are .. so it scratches very easy ... there are special techniques for cleaning that must be learned before attempting a deep cleaning .. the back side of the lens also may have a smoky coating that has to be cleaned .. again a pro is best but you can use a lens cleaning cloth and solution .. (dont spray the solution into the lens . only on the cloth .. with every thing clean your camera should be back to like new performance ..