Canon EOS REBEL T6i Instruction Manual page 373

The continuous shooting speed is slow.
Depending on the lens type, shutter speed, aperture, subject

conditions, brightness, etc., the continuous shooting speed may
become slower.
If [z3: Anti-flicker shoot.] is set to [Enable] and you shoot under a

flickering light source, the continuous shooting speed may become
slightly slower, or the continuous shooting interval may become
irregular. Also, the time lag until shutter release may be slightly longer
than usual (p.144).
If you set [Distortion] to [Enable], the continuous shooting speed will

decrease (p.141).
The maximum burst during continuous shooting is lower.
If you shoot something that has fine detail such as a field of grass, the

file size will be larger, and the actual maximum burst may be lower
than the number mentioned on page 117.
ISO 100 cannot be set.
Under [54: Custom Functions (C.Fn)], if [3: Highlight tone priority]

is set to [1: Enable], ISO 100 cannot be set. If [0: Disable] is set, ISO
100 can be set (p.339). This also applies to movie shooting (p.226).
ISO speed [H] (equivalent to ISO 25600) cannot be set.
Under [54: Custom Functions (C.Fn)], if [3: Highlight tone priority]

is set to [1: Enable], the [H] ISO speed (equivalent to ISO 25600)
cannot be selected even when [2: ISO expansion] is set to [1: On]. If
[0: Disable] is set for [3: Highlight tone priority], [H] can be set
(p.339).
The Auto Lighting Optimizer cannot be set.
Under [54: Custom Functions (C.Fn)], if [3: 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.339).
Troubleshooting Guide
373