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 #:
00025
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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16 SCIOPTICON MANUAL. in having them proceed from a point too distant to be shown. The rays of a pencil from a point 100 times further from the lens than is the image, are about paral- lel, and their focus is called the focus of parallel rays, or principal focus. A real pencil is composed of innumerable rays, and such pencils from innumerable points in the object meet and cross at the lens on their way to cor- responding points in the image, and wonderful to tell, no one is switched from the track for another, and there are no collisions. An explanation of one answers for countless millions. SPHERICAL ABERRATION. It is seen (Fig. 6) that the marginal rays d d must be more refracted, or bent, than the more central rays / /, Fig. 6. in order to meet the axial rays at / ± , and so it is seen that the margin of the lens G D has a greater refracting angle than the more central portions. But the trouble is, the refracting at the margin is overdone, so that the rays d d meet the axial ray at/ 8 instead of at/ r Hence if a ground-glass has been placed at/ t , the marginal rays which have intersected the axis at / 8 will form a circle of dispersion about f t . The diameter of this circle is called the lateral aberration, and the distance between / 8 and/ t is called the longitudinal aberration. As a con-