One of the mysteries of the English language finally explained.
1A reflecting prism in which the light is reflected on two 45° surfaces and returned parallel to the incoming beam.Compare with roof prism
- ‘Two porro prism binocular models are new, the 8x42 mm and the 10x42 mm.’
- ‘Modern roof prism designs are capable of performance just as good as a comparable porro prism design, due to current technology such as phase coating and improved reflective backing materials on the prisms.’
- ‘Bushnell's latest couples a waterproof 8x36 porro prism center-focus binocular with a laser rangefinder.’
- ‘While not as sexy as a roof prism, the porro prism is a dependable unit made for the outdoors.’
- ‘In binoculars, it has added porro prisms to its line.’
- 1.1 A pair of binoculars using two Porro prisms at right angles, resulting in a conventional instrument with objective lenses that are further apart than the eyepieces.
Named after the Italian scientist Ignazio Porro (1801–75).
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