Disable the Autofocus Assist Beam on Canon Rebel T3 Series Cameras
If you’re using your Canon Rebel T3 or T3i in dim lighting, your camera may emit an AF (autofocus)-assist beam from the built-in flash when you press the shutter button halfway — assuming that the flash unit is open, of course. This pulse of light helps the camera see its target better, improving the performance of the autofocusing system.
If you’re shooting in a situation where the AF-assist beam may be distracting to your subject or to others in the room, you can disable it. Take these steps to control this aspect of your camera:
Set the Mode dial to P, Tv, Av, M, or A-DEP.
This option is available only in these advanced exposure modes.
Display Setup Menu 3, highlight Custom Functions, and press Set.
You’re taken to the main launching pad for adjusting all Custom Functions.
Press the right or left cross key as needed to select Custom Function 6 (T3) or 7 (T3i).
Press the Set button.
Options become accessible.
Press the up or down cross key to highlight a setting.
Here are your choices:
Enable: This setting is the default and turns the AF-Assist Beam function on.
Enable External Flash Only: Choose this setting to permit an external flash unit to emit the beam but prevent the built-in flash from doing so. The external flash must be a compatible EX-series Speedlite unit.
IR AF Assist Beam Only: This setting allows an external Canon EOS-dedicated Speedlite with infrared (IR) AF-assist to use only the IR beam to aid in focusing instead of pulsing a series of small flashes like the built-in flash does when it tries to play autofocus guide dog.
One note: An external Canon Speedlite has its own provision to disable the AF-assist beam. If you turn off the beam on the flash unit, it won’t light no matter which Custom Function setting you choose.
Press the Set button.
Your chosen setting affects all advanced exposure modes. In fully automatic modes, the autofocus assist beam continues to light from the built-in flash when the camera deems it necessary. If you use an external flash that offers the assist-beam control, you can disable or enable the function through the flash itself.
Without the aid of the assist beam, the camera may have trouble autofocusing in dim lighting.