The camera monitor brightens when the DC-C1 coupler is connected.

When the DC-C1 coupler is connected to the camera, the camera monitor's brightness is fixed at maximum and cannot be adjusted.
If the monitor’s brightness becomes an issue, try the following methods that avoid using the rear monitor.

• For models with a vari-angle LCD monitor, close the monitor and use the viewfinder (if available).
• For models with a finder, select VF(Manual) under Select Finder/Monitor, and set it to display images only on the finder.
• Connect to an external monitor, select On under HDMI Info. Display, then configure the settings to prevent images from displaying on the camera monitor.
• Use the display on your smartphone by pairing the camera with your smartphone via Smartphone Connection. 
  Notes:
  • Close the vari-angle LCD monitor when using the smartphone display.
  • To connect to a smartphone, you need to install the Imaging Edge Mobile or Creators' App mobile application.