Canon EOS 80D Instruction Manual page 285

If focus is not achieved with the shooting conditions listed on the

preceding page, set the lens's focus mode switch to <MF> and focus
manually.
Depending on the lens used, focusing may take longer or correct focus

may not be achieved. For details, refer to the Canon website.
If you shoot a peripheral subject and it is slightly out of focus, aim the

center AF point or zone over the subject to focus, focus again and then
take the picture.
The AF-assist beam will not be emitted. However, if an EX-series

Speedlite (sold separately) equipped with an LED light is used, the LED
light will turn on for AF-assist when necessary.
In magnified view, achieving focus becomes more difficult due to camera

shake. Using a tripod is recommended.
Focusing with AF (AF Method)
285