Elementary optics and applications to fire control instruments (1922)
United States. Army. Ordnance Dept · Washington, Govt. Print. Off. · leaf 49
Fig. 49.—Curvature of field. … jO.—Dislurli the field is curved and for different lenses the curvature may be fromor toward the center. The distortion is termed *barrel-shaped in 46 the first case and hourglass or pincushion in the second. Thetwo lower diagrams show the appearance of a net of orthogonal lineswhen imaged by a…
Optics · Optical instruments · Fire control (Gunnery) -- Optical equipment
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