Enabling Mirror Lockup on the Canon EOS 77D
One component in the optical system of a dSLR camera is a mirror that moves when you press the shutter button. The vibration caused by the mirror movement can result in image blur when you use a very slow shutter speed, shoot with a long telephoto lens, or take extreme close-ups. To eliminate this possibility, your Canon EOS 77D camera offers mirror lockup, which delays the shutter release a little longer than normal so that the picture isn’t recorded until after the mirror movement is completed.
Of course, you should also mount the camera on a tripod so that camera shake caused by handholding the camera doesn’t create blur.
You can take advantage of mirror-lockup shooting only in the P, Tv, Av, or M exposure modes. Enable it through Custom Function 10, as shown here.
Mirror-lockup shooting requires a special picture-taking process: Press the shutter button once to lock up the mirror, release the button, and then press it all the way down again to take the picture.