Depth-of-Field Preview Button Does Not Work (EOS 6D Mark II)
Solution
If you press the depth-of-field preview button but can not stop down the lens to the current aperture setting, it may be possible that the depth-of-field preview button has been assigned some other function.
To be able to check the depth of field (range of acceptable focus) by pressing the depth-of-field preview button, follow the steps below and reassign the "Depth-of-field preview" function.
1. Set the camera's power switch to <ON>.
2. Set the Mode Dial to a Creative Zone mode.
3. Press the <MENU> button to display the menu screen.
4. Under the [ 
] tab, select [C.Fn III: Operation/Others], then press < 
>.
] tab, select [C.Fn III: Operation/Others], then press < >.
5. Select [4: Custom Controls], then press < >.
>.
6. The Custom Controls setting screen will appear, so select [ 
] and press < >.
] and press < >.
7. When the screen for assigning the depth-of-field preview button's function appears, select [ 
], then press < >.
], then press < >.
8. When the depth-of-field preview button's function is set, the screen in step 6 will reappear. Press the <MENU> button three times to exit the setting.
NOTE
With the screen in step 6 displayed, you can press the < 
> button to revert the Custom Control settings to their defaults. Note that the [ C.Fn III-4: Custom Controls] settings will not be canceled even if you select [ : Clear all Custom Func. (C.Fn)].
> button to revert the Custom Control settings to their defaults. Note that the [ C.Fn III-4: Custom Controls] settings will not be canceled even if you select [ : Clear all Custom Func. (C.Fn)].