Canon MARK IV User Manual (en)

Bulb Exposures
If you take a picture without looking at 
the viewfinder, light entering the 
eyepiece can throw off the exposure. To 
prevent this, slide the eyepiece shutter 
lever as shown by the arrow to shutter 
the eyepiece.
You need not shutter the eyepiece during 
Live View shooting or movie shooting.
You can connect Remote Switch RS-80N3 or Timer Remote Controller 
TC-80N3 (both sold separately) or any EOS accessory equipped with 
an N3-type terminal to the camera and shoot with it.
To operate the accessory, refer to its instruction manual.
Open the terminal cover.
Open the upper terminal cover.
Connect the plug to the remote 
control terminal.
Connect the plug as shown in the 
To disconnect the plug, grasp the 
plug’s silver part and pull out.
Using the Eyepiece Shutter
Connecting the Remote Switch