. Optical projection : a treatise on the use of the lantern in exhibition and scientific demonstration. Fia. 15.—Spherical Aberration a plane; or conversely, the diagram or picture m m must bedrawn upon a concave surface to produce a flat image mm, anexpedient actually employed in early solar Fig. of Image The curved image maybe more or less flattened, as it iacalled, by adopting a meniscus form for the lens, as shown infig. 14 by the various achromatics b, c, e. But we are nowconfronted with another result of aberration, in the form of the THE PARTS OF A LANTERN
. Optical projection : a treatise on the use of the lantern in exhibition and scientific demonstration. Fia. 15.—Spherical Aberration a plane; or conversely, the diagram or picture m m must bedrawn upon a concave surface to produce a flat image mm, anexpedient actually employed in early solar Fig. of Image The curved image maybe more or less flattened, as it iacalled, by adopting a meniscus form for the lens, as shown infig. 14 by the various achromatics b, c, e. But we are nowconfronted with another result of aberration, in the form of the THE PARTS OF A LANTERN 27 image. In fig. 16 let s represent the slide, a true image ofwhich we wish to produce. Then b represents what is calledthe • barrel distortion, the usual distortion of a single we correct this merely for flatness of field, which is theeasiest and most obvious error to correct, we usually get thefigure over-corrected, producing the hour-glass distortiondenoted by h. Either distortion, if perceptible, is simplyintolerable in architectural subjects, lines of type, or diagramswhich may contain straight lines or circles. The correction of these various errors in lenses of moderatefocus is a task of no little difficulty. The chromatic correction is a comparatively simple affair, needing simpl
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Keywords: ., bookauthorwrightle, bookcentury1900, bookdecade1900, bookyear1906
