Coating

A layer applied to lens glass surfaces to alter their refractive characteristics. Multi-coating uses more than one coating to correct for different behaviour by different wavelengths (colours) of light.

Parallax

The different image content that results from slightly different viewpoints. What you see isn't exactly what you get.

Pentaprism

A five-sided prism (obviously!) that provides an eye-level, right-way up, left to right correct view of the subject.

Taking lens

In a twin lens reflex camera, the lower lens used to expose the film.

Viewing lens

In a twin lens reflex camera, the upper lens that is used for composition and focusing..

WLF

Waist-level finder. The basic `flip-up and look down' finder type. Consists of a folding light shield around the camera focussing screen. Image is right-way up, but left to right reversed.

Paramender

Mamiya device to move the camera at right angles to the lens axis and parallel to the lens board by 50mm (2"). This moves the taking lens to the viewing lens position to correct parallax at close distance.

Porrofinder

A finder that uses mirrors to achieve a right-way up, left to right correct eye level image. Similar in effect to a pentaprism.

Rack and pinion

A gearing mechanism that uses a toothed bar or track in conjunction with a toothed roller at right angles to the bar.