Canon EOS 77D User Manual - Page 406

3 Custom Function Setting ItemsN C.Fn-9 Viewfinder display illumination You can set whether the AF points in the viewfinder will light up in red when focus is achieved. 0: Auto The AF points automatically light up in red under low light. 1: Enable The AF points light up in red regardless of the ambient light level. 2: Disable The AF points do not light up in red. When AI Servo AF is set, the AF points will not light up in red even when focus is achieved.  When you press the or button, the AF points will be illuminated in red regardless of this setting.  The aspect ratio lines (p.156), and the electronic level, grid, and flicker detection set with [52: Viewfinder display] will also light up in red. C.Fn-10 Mirror lockup 0: Disable 1: Enable You can prevent the camera vibration blur due to the mechanical vibrations (mirror shock) inside the camera during shooting with super telephoto lenses or shooting close-ups (macro photography). See page 209 for the mirror lockup procedure. 406