Canon EOS-1D X Mark III EOS-1DX Mark III Advanced User Guide - Page 112

Depth-of-Field Preview Press the depth-of-field preview button to stop down the lens to the current aperture setting and check the area in focus (depth of field). Note The larger the aperture value, the wider the area (from the foreground to the background) in focus, but the darker the viewfinder display. The depth-of-field effect is readily apparent on the Live View image as you change the aperture value and press the depth-of-field preview button ( ). Exposure is locked (AE lock) as you hold down the depth-of-field preview button. Pressing the depth-of-field preview button when a Speedlite 470EX-AI is attached with the < > switch set to < > (full-auto) starts AI.B full-auto distance measurement. 112