Canon EOS REBEL T6i Instruction Manual page 164

Mirror Lockup to Reduce Camera ShakeK
Do not point the camera toward an intense light source, such as the sun

or an intense artificial light source. Doing so may damage the image
sensor or the camera's internal components.
In very bright light, such as at the beach or a ski slope on a sunny day,

take the picture promptly after mirror lockup is stabilized.
If you use the self-timer and bulb exposure in combination with a mirror

lockup, keep pressing the shutter button completely (self-timer delay
time + bulb exposure time). If you let go of the shutter button during the
self-timer countdown, there will be a shutter-release sound, but no
picture will be taken.
During mirror lockup, shooting function settings and menu operations,

etc. are disabled.
If you use flash, the red-eye reduction lamp will not light up (p.167).

Even if you set the drive mode to <i>, <M>, or <q>, the camera

will still shoot in single shooting mode.
When [z3: High ISO speed NR] is set to [Multi Shot Noise

Reduction], four continuous shots will be taken for the single picture
regardless of the [9: Mirror lockup] setting.
If 30 sec. elapse after the mirror is locked up, it will go back down

automatically. Pressing the shutter button completely again locks up the
mirror again.
164