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 #:
00029
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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20 SOIOPTICON MANUAL. UNEQUAL ILLUMINATION. We can see that the brightness of an image decreases from the centre towards the margin. The diameter of the pencil g g passing through the lens parallel to its axis, is of the same size as the opening of the stop £, and exceeds the diameter of the oblique bundle of rays. Besides, the oblique rays lose considerable light by re- flection, which may in part be re-reflected upon the image, detracting from its distinctness. With a short exposure in the camera, this unequal illumination causes an under- exposure at the margin. In the Sciopticon it is even exaggerated by the reflector, but we generally wish the objects occupying the central portion of the "field of view" to stand out more clearly in the illuminated disk. CORRECTIONS 1JS THE EYE. Spherical aberration and distortion in the eye are corrected (it Is believed) by the greater density of the crystalline lens about its centre than towards the margin, where the refracting angle would otherwise be too great. Chromatic aberration is corrected by the combined