Elementary optics and applications to fire control instruments (1922)
United States. Army. Ordnance Dept · Washington, Govt. Print. Off. · leaf 33
fore bedefined as the distance from thevertex of the mirror to the imageformed of an object at an infinitedistance. Conversely, if the point O ap-proaches the mirror, u increasesand becomes infinite when u equals-/. A source at O, figure 30, thensends forth rays which, after re-flection, are… … Fig. 31.—Projection by a spherical and parabolicmirror. 30 If we wish to illuminate a distant object, it is advantageous toplace the source at the focus of a concave mirror, as sho^\^l in figure30. All the rays which fall upon the mirror are then projected ina common direction and fall upon the…
Optics · Optical instruments · Fire control (Gunnery) -- Optical equipment
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