Canon eos rebel t1i - Manual (Page 205)

205
Troubleshooting Guide
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.
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).
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).
If you shoot continuously with the built-in flash at short intervals, the
flash might stop operating to protect the flash unit.
The maximum burst during continuous shooting is lower.
ISO 100 cannot be set.
When I use the <f> mode with flash, the shutter speed
becomes slow.
The built-in flash does not fire.