Not to put too fine of a point on it, Jen, but the sensor in a DSLR ISN'T the equivalent of the mirror in an SLR body. DSLRs use a mirror the same as an SLR. That's the only way you get the image coming in through the lens up to the viewfinder in an SLR-type camera body design. The sensor sits behind the mirror and is the digital equivalent of the film in an SLR body if you want to talk in terms of equivalents. The sensors in DSLRs vary in size from 24x36 mm (the size of a 35 mm film frame) downward depending on the body. There are also several different types of sensors in use, CMOS happens to be what Canon is currently using. When you trip the shutter in an SLR or DSLR, the mirror flips up out of the way exposing the film or sensor, as the case may be, to the light coming in through the lens. The only exception are a few SLR camera bodies that use what is known as a pellical mirror... you change the charge on the mirror surface and it goes from being a mirror to optically transparent and doesn't have to be flipped up out of the way, allowing you to shoot more frames/sec. I don't think anyone has yet produced a DSLR body with a pellical mirror.