Blinder

A blinder is a physical shield attached to or surrounding the oculars of a stereoscope. Its function is to exclude external light and visual distractions, thereby improving image quality of the stereoview.

Blinders can be implemented in various ways. Rotatable eyecups attached to the oculars are primarily found on box-type viewers and tabletop stereoscopes. The Holmes–Bates stereoscope uses a curved shield that covers both oculars.