Using The Eyepiece Cover - Canon EOS 5DS Instruction Manual

Using the Eyepiece Cover

When you use the self-timer, bulb, or a remote switch and do not look
through the viewfinder, stray light entering the viewfinder can cause the
picture to look dark. To prevent this, use the eyepiece cover (p.35)
attached to the camera strap.
During Live View shooting and movie shooting, it is not necessary to
attach the eyepiece cover.
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Detach the eyecup.
1
While grasping both sides of the
eyecup, slide it upward to detach it.
Attach the eyepiece cover.
2
Slide the eyepiece cover down into
the eyepiece groove to attach it.
After you finish shooting, detach the
eyepiece cover and attach the
eyecup.