Canon EOS REBEL T7i Instruction Manual page 201

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.
When shooting with mirror lockup, if you use both the self-timer and bulb

exposures, keep pressing the shutter button completely (for 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, menu operations, etc.

are disabled.
When you use flash, the red-eye reduction lamp will not light up (p.205).

Even if you set the drive mode to <o>, <i>, or <q>, the camera

will still shoot in single shooting mode.
When [z4: High ISO speed NR] is set to [Multi Shot Noise

Reduction], four consecutive shots will be taken for a single picture
regardless of the [10: Mirror lockup] setting.
If approx. 30 sec. elapse after the mirror has locked up, it will go back

down automatically. Pressing the shutter button completely locks up the
mirror again.
When shooting with mirror lockup, using a tripod and Remote Switch RS-

60E3 (sold separately, p.413) is recommended.
Mirror Lockup to Reduce Camera Vibration BlurN
201