Canon EOS Rebel T1i EOS REBEL T1i/EOS 500D Instruction Manual - Page 205

Troubleshooting Guide The maximum burst during continuous shooting is lower. Set the [7 Custom Functions (C.Fn)] menu's [High ISO speed noise reduction] to [Standard], [Low], or [Disable]. If it is set to [Strong], the maximum burst during continuous shooting will decrease (p.185). If you shoot a subject which has fine detail (field of grass, etc.), the file size will be larger and the actual maximum burst will be lower than the number mentioned on page 70. ISO 100 cannot be set. Under the [7 Custom Functions (C.Fn)] menu, if [Highlight tone priority] is set to [Enable], ISO 100 cannot be set. When [Disable] is set, ISO 100 can be set (p.186). When I use the mode with flash, the shutter speed becomes slow. If you shoot night scenes, the shutter speed becomes slow automatically (slow-sync shooting) so that both the subject and background are properly exposed. If you do not want a slow shutter speed to be set, set the [7 Custom Functions (C.Fn)] menu's [Flash sync. speed in Av mode] to 1 or 2 (p.184). The built-in flash does not fire. If you shoot continuously with the built-in flash at short intervals, the flash might stop operating to protect the flash unit. 205