Snelling, Henry Hunt, 1816-1897 · [New York : W.B. Smith] · leaf 263
flat field. To manufacture a lens whichshall effect this, is a task of some difficul-ty ; but byattention to the two facts, thata lens, one surface of which is a section ofan ellipse, and the other of a circle struckfrom the farthest of the two foci of thatellipse, as in Fig. 6, produces no aberra- … tion, much may be effected. A meniscuslens, therefore, with a convex surface, partof an ellipsoid, the focal distmce of whichcoiacides with its farther focus, and a eon-cave surface, part of a sphere, whose cen- tre is that foeus, will meet all our require-ments. The mechanical difficulties…
Photography · Art and photography
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