Snelling, Henry Hunt, 1816-1897 · [New York : W.B. Smith] · leaf 263
l be brilliant and welldefined around the centre, the light be-coming fainter towards the edge, and atlength passing into a cloudy halo, exhibit-ing the prisma ic colors. This is calledspherical abberation, and to it is due thatwant of distinctness which commonly isfound around the edges of… … 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-
Photography · Art and photography
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