Optical Type

The optical design of a binocular or spotting scope. A binocular can be either a porro prism (whose objective lenses are off-set and spaced further apart than the eyepieces) or a roof prism (whose objective lenses are in line with the eyepieces). A spotting scope can be either a porro prism or roof prism refractor or a catadioptric (a combination of lenses, mirrors, and prisms).

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