Canon REBEL T3I EOS 600D User Manual page 281

The maximum burst during continuous shooting is lower.
Under [7 Custom Functions (C.Fn)], set [5: High ISO speed noise
reduction] to [Standard], [Low], or [Disable]. If it is set to [Strong],
the maximum burst during continuous shooting will greatly decrease
(p.254).
If you shoot something that has fine detail (field of grass, etc.), the file
size will be larger and the actual maximum burst might be lower than
the number mentioned on page 76.
ISO 100 cannot be set.
Under [7 Custom Functions (C.Fn)], if [6: Highlight tone priority]
is set to [1: Enable], ISO 100 cannot be set. If [0: Disable] is set, ISO
100 can be set (p.254). This also applies to movie shooting (p.159).
The Auto Lighting Optimizer cannot be set.
Under [7 Custom Functions (C.Fn)], if [6: Highlight tone priority]
is set to [1: Enable], the Auto Lighting Optimizer cannot be set. If [0:
Disable] is set, the Auto Lighting Optimizer can be set (p.254). This
also applies to movie shooting (p.162).
ISO speed [H] (ISO 12800) cannot be set.
Under [7 Custom Functions (C.Fn)], if [6: Highlight tone priority]
is set to [1: Enable], the [H] ISO speed cannot be selected even when
[2: ISO expansion] has been set to [1: Enable]. If [0: Disable] is set,
[H] can be set (p.252).
Troubleshooting Guide
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