Canon EOS Rebel T3i EOS REBEL T3i / EOS 600D Instruction Manual - Page 98

f: Changing the Depth of Field D Using the Built-in Flash To obtain a correct flash exposure, the flash output will be set automatically to match the set aperture (autoflash exposure). The shutter speed will be set automatically between 1/200 sec. - 30 sec. to suit the scene's brightness. In low light, the main subject is exposed with the automatic flash, and the background is exposed with a slow shutter speed set automatically. Both the subject and background look properly exposed (automatic slow-speed flash sync). If you are handholding the camera, keep it steady to prevent camera shake. Using a tripod is recommended. If you do not want a slow shutter speed to be used, set [3: Flash sync. speed in Av mode] to [1: 1/200-1/60 sec. auto] or [2: 1/200 sec. (fixed)] in [7 Custom Functions (C.Fn)] (p.252). Depth of Field PreviewN The aperture opening (diaphragm) changes only at the moment when the picture is taken. Otherwise, the aperture remains fully open. Therefore, when you look at the scene through the viewfinder or LCD monitor, the depth of field will look narrow. When you press the depth-of-field preview button, you can see the actual depth of field before you shoot. While looking at the Live View image (p.124) and holding down the depth-offield preview button, you can change the aperture and see how the depth of field changes. 98