Digital SLR Camera Basics

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optical low-pass filter (OLPF)

A filter fitted in front of the image sensor to reduce moiré by filtering ultraviolet and infrared light.

See also: moiré

optical viewfinder

The window in which the photographer frames the subject and checks focus. An electronic display such as a monitor can also be used as a viewfinder; in contrast to such electronic viewfinders, optical viewfinders consist of only of optical components such as lenses, prisms, and mirrors.

optimal exposure

The exposure that will produce a photograph with optimal brightness.

optional flash unit (Speedlight)

A flash unit that can be mounted on the camera accessory shoe. Optional flash units are generally more powerful than built-in flash units and have features adapted specifically to flash photography. Even if the camera is equipped with a built-in flash, optional flash units can provide lighting and features not supported by the built-in flash.

overexposure

Exposure greater than the optimal amount. Photographs that are overexposed are brighter than expected.