The five advanced exposure modes of the Canon EOS Digital Rebel XSi/450D give you more control over your camera settings than you get using the automatic modes. In P, Tv, Av, and M modes, you can adjust aperture (f-stop) to manipulate depth of field (the zone of sharp focus) and adjust shutter speed to determine whether moving objects appear sharply focused or blurry. In all five modes, you also can tweak color, ISO (light sensitivity), and exposure.