Canon EOS-1D X Mark III EOS-1DX Mark III Advanced User Guide - Page 234

Exposure Lock (AE Lock) AE Lock Effects You can lock the exposure when you want to set the focus and exposure separately or when you will take multiple shots at the same exposure setting. Press the < > button to lock the exposure, then recompose and take the picture. This is called AE lock. It is effective for shooting backlit subjects, etc. 1. Focus on the subject. Press the shutter button halfway. The exposure value will be displayed. 2. Press the < > button ( ). A < > icon is displayed in the viewfinder, indicating that the exposure is locked (AE lock). Each time you press the < > button, the current exposure setting is locked. 234