Elementary optics and applications to fire control instruments (1922)
United States. Army. Ordnance Dept · Washington, Govt. Print. Off. · leaf 27
two faces form the roof of the prism. Thelower prism of the panoramic sight and the prism used in the right-angle telescope of antiaircraft fire-control apparatus are of this type.This prism when inserted in a telescopic system bends the axis of thetelescope through 90° and also erects the image.… … Fig. 20.—Second type of Porro system. Fig. 21.—Right angle prism with roof. is not reverted. This prism is one of the most difficult to manu-facture, as the angle between the two inclined faces can not differfrom 90° by more than a few seconds if the prism is to function satis-factorily. The angle…
Optics · Optical instruments · Fire control (Gunnery) -- Optical equipment
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