Elementary optics and applications to fire control instruments (1922)
United States. Army. Ordnance Dept · Washington, Govt. Print. Off. · leaf 49
45 image, if it is to be in focus on the whole phite at once, shouldalso be plane. A field without curvature is termed flat. Flatnessof field is secured bythe use of particularkinds of glass andby means of dia-phragms whichcause the raysforming images atthe edge and cen-ter of the field to traverse… … Fig. 49.—Curvature of field.
Optics · Optical instruments · Fire control (Gunnery) -- Optical equipment
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