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 #:
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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ON PROJECTION ii through the focussing lens ; and to understand this is most necessary to any successful projection which may be the least out of the beaten track. We shall see hereafter that, for want of understanding this, even slides and diagrams are often badly shown, and unnecessary expense is often incurred. This understood, however, it is obvious that a much better arrangement in several respects must be to interpose the condensing lens between the slide or object and the light, as in fig. 7. The otherwise wasted divergent rays E A and E B are still bent in so as to pass through the focussing lens, L ; but a large part of the heat is borne by the lens c, and the slide or apparatus so far shielded ; and the focussing lens, L, ,8 FIG. 7 has no distorting medium between it and the object. This, therefore, is the arrangement now always used in instruments of a serious kind. 6. Management of the Rays.—We now understand exactly why the margin of our slide in the first experiment was not illuminated upon the screen, until the light was drawn back from its usual position. There was a condenser, and the rays were sufficiently converged to pass through the lens—say a circle of two inches diameter—in the usual manner. But they were not sufficiently converged for any appreciable rays passing through the margin of the slide, to pass through the small central pinhole. By drawing back the light, they were