Glossary Terms

Viewfinder Blackout is a problem in single-lens reflex (and also view cameras) where the viewfinder image is lost during the exposure- so the photographer cannot see the exact image at the moment the photograph is taken.

This is caused by using the same lens for viewing as for taking. In an SLR, a mirror is used to reflect the lens' image into the viewfinder; this mirror must be moved aside to allow light through the shutter and onto the film or image sensor. Whilst the mirror is in the taking position, the viewfinder is dark.

Most SLRs feature an Instant-return mirror, and so the viewfinder image returns immediately after taking the photograph, however, early SLRs had either a manually-returned mirror, or one that was reset by winding the film.

A few cameras, such as the Canon Pellix, have avoided this problem by using a semi-silvered mirror - called a pellicle - which can stay in the light path during exposure. This also removes the mirror slap problem.