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

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 #:
00026
Language:
English
Collection:
Books
Format:
Books
Contributor:
University of California Libraries
Sponsor:
MSN
Coordinator:
Media History Digital Library
Description:
Date Added:
July 19, 2022
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SCIOPTICON MANUAL. 17 sequence of this want of coincidence between the foci of the central and marginal rays the picture on the screen, or ground-glass, will appear blurred and ill defined. We can conceive of a lens with a gradually lessening degree of convexity towards the margin, causing the foci to coincide, but lenses cannot well be ground in this form. The crystalline lens in the eye is supposed to cause the foci to coincide by an increase of density towards its centre, but such an arrangement of matter would be impracticable in art. Much is gained by re- versing the lens, for spherical aberration is four times as great when the parallel rays enter its plane surface, as when they enter its convex surface. Much is gained by a combination of lenses so that the refracting angle may be less in each. Were the mar- ginal rays d d cut off by a stop, the aberration would be less, as we can see by tracing them in the diagram, but the illumination would also be less by so much. DISTORTION. When we focus with a single lens with a front stop C Fig. 7. sharply on a square, A (Fig. 7) the resulting picture will not appear square, but barrel-shaped, as at B. When we