Canon EOS Rebel T2i EOS REBEL T2i / EOS 550D Instruction Manual - Page 194

3 Custom Function SettingsN C.Fn-6 Highlight tone priority 0: Disable 1: Enable Improves the highlight detail. The dynamic range is expanded from the standard 18% gray to bright highlights. The gradation between the grays and highlights becomes smoother. With setting 1, the [Disable] setting automatically takes effect for the Auto Lighting Optimizer (p.103) and it cannot be changed. With setting 1, noise may become slightly more pronounced than usual. With setting 1, the settable ISO speed range will be 200 - 6400. Also, the icon will be displayed on the LCD monitor and in the viewfinder when highlight tone priority is enabled. C.Fn III: Autofocus/Drive C.Fn-7 AF-assist beam firing The AF-assist beam can be emitted by the camera's built-in flash or by an external, EOS-dedicated Speedlite. 0: Enable 1: Disable The AF-assist beam is not emitted. 2: Enable external flash only If an external, EOS-dedicated Speedlite is attached, it will emit the AFassist beam when necessary. The camera's built-in flash will not fire the AF-assist beam. 3: IR AF assist beam only Among EOS-dedicated Speedlites, only those which have an infrared AF-assist beam will be able to emit the beam. This prevents any Speedlite which uses a series of small flashes (like the built-in flash) from firing the AF-assist beam. If the external, EOS-dedicated Speedlite's [AF-assist beam firing] Custom Function is set to [Disabled], the Speedlite will not emit the AF-assist beam even if the camera's C.Fn-7-0/2/3 is set. 194