The sciopticon manual, explaining lantern projection in general, and the sciopticon apparatus in paricular (1877)

Page scan 00028 from The sciopticon manual, explaining lantern projection in general, and the sciopticon apparatus in paricular

Record Details:

Title:
The sciopticon manual, explaining lantern projection in general, and the sciopticon apparatus in paricular
Date:
1877
Publisher:
Philadelphia, J. A. Moore
Volume:
The sciopticon manual, explaining lantern projection in general, and the sciopticon apparatus in paricular
Leaf #:
00028
Language:
English
Collection:
Books
Format:
Books
Contributor:
University of California Libraries
Sponsor:
MSN
Coordinator:
Media History Digital Library
Date Added:
July 19, 2022
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SCIOPTICON MANUAL. 19 CHROMATIC ABERRATION, OR DISPERSION OF COLOR. White light is separated by a prism into the seven primary colors; violet, indigo, blue, green, yellow, orange, red. As a lens is analogous to a system of prisms, and as violet is more refrangible than red, the violet rays v v (Fig. 9) will intersect the axis closer to the lens than the red rays r r. This error is corrected by combining a concave lens of flint-glass with a convex lens of crown- glass, so as to neutralize their contrary dispersions. The concave flint-glass lens / (Fig. 12), which has great dispersive power in proportion to its curves, diverges the violet more than the red, while the convex crown-glass lens converges the violet more than the red, so we have in both combined an achromatic convex lens. As the chemical rays are in the violet end of the spectrum, the photographer may succeed with an im- Flg. 9. perfectly corrected lens by having the sensitive plate a little nearer the lens than the focus of luminous rays on the ground-glass would indicate. Lenses without chro- matic aberration are called achromatic. The term aplanatic means without wandering, and may apply to lenses corrected of both spherical and chromatic aber- ration.