Canon EOS Rebel T2i EOS REBEL T2i / EOS 550D Instruction Manual - Page 193

3 Custom Function SettingsN When 1 or 2 is set, high-speed sync cannot be used with an external Speedlite. C.Fn II: Image C.Fn-4 Long exposure noise reduction 0: Off 1: Auto For 1 sec. or longer exposures, noise reduction is performed automatically if noise typical of long exposures is detected. This [Auto] setting is effective in most cases. 2: On Noise reduction is performed for all exposures of 1 sec. or longer. The [On] setting may be effective for noise that cannot be detected or reduced with the [Auto] setting. With setting 1 and 2, after the picture is taken, the noise reduction process may take the same amount of time as the exposure. You cannot take another picture until the noise reduction process is completed. At ISO 1600 and higher, noise might be more pronounced with setting 2 than with setting 0 or 1. With setting 2, if a long exposure is shot during Live View display, "BUSY" will be displayed during the noise reduction process. The Live View display will not appear until the noise reduction is completed. (You cannot take another picture.) C.Fn-5 High ISO speed noise reduction Reduces the noise generated in the image. Although noise reduction is applied at all ISO speeds, it is particularly effective at high ISO speeds. At low ISO speeds, the noise in the shadow areas is further reduced. Change the setting to suit the noise level. 0: Standard 1: Low 2: Strong 3: Disable With setting 2, the maximum burst for continuous shooting will greatly decrease. 193