What is a viewfinder shutter or cover for?
High-end Canon SLRs have a flip-down lever by the viewfinder that lets a mechanical shutter swing down and physically cover off the back of the viewfinder so you can t look through it anymore. Canon SLRs which lack this feature usually ship with a detachable plastic or rubber cover either attached or built into the camera strap. What s this for? Well, the light metering sensors in an SLR are located inside the top hump of the camera as part of the viewfinder assembly. They record light levels inside the viewfinder. And when you re peering through the viewfinder then most of the light entering the camera is coming in through the lens. However, when you re not looking through the viewfinder (thereby physically blocking it) then light can enter the camera from the viewfinder itself, throwing off the light meter. This is particularly a problem if you re using the camera on a tripod in self-timer mode. Viewfinder shutters, therefore, reduce the risk of metering error from stray light enteri
