^Porro – prisms

A Porro – prisms is a totally reflected is a right handed isosceles prisms having ∠C = 42⁰, μ = 1.5 and ∠i = 45⁰.  These prisms are used to bend light by 90º or by 180º & to invert images without changing their size. Following are few advantages of TRPs over plane mirrors.

• Unlike plane mirror, do not require silvering.
• Almost 100 % reflection is possible in TRP (where as in case of a good plane mirror it is never more than 95%). Hence comparatively brighter image is produced.
• When used for a long time, the silvered face of mirror deteriorates which reduces the quality of the image. (in TRP there is no such deterioration).