The Canon EOS-40D’s new live preview mode is a hot feature, giving you through-the-lens viewing on the 3-inch LCD, with a full data display under the image.
Unlike the 1D Mark III, the 40D’s AF works in live preview. It’s similar to the live preview AF on several Olympus and Panasonic DSLRs, and causes a short screen blackout while the mirror flips down and the camera focuses. Not the ideal AF method, but useful in some situations.