How to Enable Mirror Lockup on the Rebel t5i
One component in the optical system of the Rebel t5i 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 camera offers mirror lockup. When you enable this feature, the mirror movement is completed well before the shot is recorded, thus preventing mirror-related camera shake.
Mirror-lockup shooting requires a special picture-taking process:
Set the Mode dial to P, Tv, Av, or M.
Mirror lockup isn’t available in the other exposure modes.
Set Custom Function 5, Mirror Lockup, to Enable.
Frame your shot.
If you're using manual focusing, set focus.
Press and hold the shutter button halfway.
This step engages autoexposure and autofocusing, if you're using that focusing method.
Press the shutter button all the way down to lock up the mirror. Then release the button.
You can no longer see anything through the viewfinder now. Don’t panic — that’s normal. The mirror’s function is to display in the viewfinder the scene that the lens will capture, and mirror lockup prevents it from serving that purpose.
Press the shutter button all the way again.
The camera takes the picture.
Using a tripod is critical to getting shake-free shots in situations that call for mirror lockup. For more protection, set your camera to the Self-Timer: 2 second mode and take your hands off the camera after you press the shutter button in Step 6. The picture is taken two seconds after mirror lockup occurs. If you own a remote control unit, you can use it to trigger the shutter release.
A couple more fine points:
Drive mode: Even if the Drive mode is set to Continuous or Self-Timer: Continuous, the camera behaves as it does in Single mode: You get one picture for each press of the shutter button.
Auto shutoff: If you don't press any buttons for 30 seconds after you lock up the mirror, it automatically flips back down.