Canon EOS-1D Mark IV EOS-1D Mark IV Instruction Manual - Page 107

d: Program AE 4 Take the picture. Compose the shot and press the shutter button completely. If the "30"" shutter speed and the maximum aperture blink, it indicates underexposure. Increase the ISO speed or use flash. If the "8000" shutter speed and the minimum aperture blink, it indicates overexposure. Lower the ISO speed or use an ND filter (sold separately) to reduce the amount of light entering the lens. During automatic AF point selection (p.97) or manual AF point selection with expanded AF points (p.222), multiple AF points might light up simultaneously. About Program Shift In the Program AE mode, you can freely change the shutter speed and aperture combination (Program) set automatically by the camera while maintaining the same exposure. This is called Program shift. To do this, press the shutter button down halfway, then turn the dial until the desired shutter speed or aperture value is displayed. Program shift is canceled automatically after the picture is taken. Program shift is not possible with flash. 107