Canon MARK IV User Manual (en)

: Aperture-Priority AE
Press the depth-of-field preview button 
to stop down the lens to the current 
aperture setting. You can check the 
depth of field (range of acceptable focus) 
through the viewfinder.
Depth-of-Field Preview
If the “30"” shutter speed blinks, it indicates 
Turn the <6> dial to set a larger aperture 
(lower f/number) until the shutter speed 
blinking stops or set a higher ISO speed.
If the “8000” shutter speed blinks, it 
indicates overexposure.
Turn the <6> dial to set a smaller 
aperture (higher f/number) until the shutter 
speed blinking stops or set a lower ISO 
Aperture Display
The higher the f/number, the smaller the aperture opening will be. The 
apertures displayed will differ depending on the lens. If no lens is attached to 
the camera, “00” will be displayed for the aperture.
A higher f/number will make more of the foreground and background fall 
within acceptable focus. However, the viewfinder will look darker.
If the depth of field is difficult to discern, hold down the depth-of-field 
preview button while turning the <6> dial. The depth of field can be 
clearly seen with the Live View image (p.126).
The exposure will be locked (AE lock) while the depth-of-field preview 
button is pressed.