Optical projection: a treatise on the use of the lantern in exhibition and scientific demonstration (1906)

Record Details:

Title:
Optical projection: a treatise on the use of the lantern in exhibition and scientific demonstration
Date:
1906
Author:
Wright, Lewis, 1838-1905
Publisher:
London, New York, Bombay : Longmans, Green and Co.
Volume:
Optical projection: a treatise on the use of the lantern in exhibition and scientific demonstration
Leaf #:
00045
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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30 OPTICAL PROJECTION diameter is a task of tremendous optical difficulty, and the wonder is that such approximation to it has been attained. 16. Focus and Diameter of Objectives.—The proper focus of an objective of course depends upon the size of disc which is required to be covered by a slide at a given distance, and the range of foci suitable in a set of objectives, will depend upon the range of work, or variety in size of rooms, it is intended to provide for. This is dealt with in detail in Chapter VIII. Here it is only necessary to mention the matter in connection with the diameter of objectives. We have seen that brilliance of image depends upon sending the rays collected on the FIG. 19.—Scattering of Rays object through the objective, and we know that only from a radiant point could the rays be alike converged into a given area at different distances from the condenser. With, say, a luminous spot of f-inch diameter, the light cannot be con- verged save into an image, proportionate in size to the conjugate focus of convergence, as shown in fig. 19. Hence, while all the light can easily be converged into a small lens at a few inches from the slide, at twelve inches it is another matter: the body of rays must spread out more, and require a larger lens to utilise them in the image. Besides this, a certain amount of the rays are irregularly ' scattered ' by the