Canon EOS Rebel SL1 18-55mm IS STM Kit Instruction Manual page 148

Mirror Lockup to Reduce Camera ShakeN
In very bright light, such as at the beach or a ski slope on a sunny day,
take the picture promptly after mirror lockup.
Do not point the camera toward the sun. The sun's heat can damage the
camera's internal components.
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.
Even if you set Drive/self-timer 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 [5: Mirror lockup] setting.
If 30 seconds elapse after the mirror has locked up, it will go back down
automatically. Pressing the shutter button completely again locks up the
mirror again.
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