The book of lantern ; being a practical guide to the working of the optical (1888)

Record Details:

Title:
The book of lantern ; being a practical guide to the working of the optical
Date:
1888
Publisher:
London : Wyman & Sons
Volume:
The book of lantern ; being a practical guide to the working of the optical (or magic) lantern ; with full and precise directions for making and colouring lantern pictures
Leaf #:
000108
Language:
English
Collection:
Books
Format:
Books
Contributor:
University of California Libraries
Sponsor:
MSN
Coordinator:
Media History Digital Library
Date Added:
July 19, 2022
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THE BOOK OF THE LANTERN. 95 frame, it should be strong; for if the sheet is tightly- stretched, as it ought to be, there will be a very heavy strain upon its support. Perhaps the best wood for the purpose is bamboo, which combines the qualities of extreme lightness with great strength. I believe that bamboo frames can now be obtained commercially. The rule for finding the correct distance between lantern and sheet is to add one to the number of times enlargement required, and multiply by the equivalent focus of the lens used. If, for instance, a slide measures 3 inches, and it is desired to cover a screen 10 feet across, the scale of enlargement is 40 times : and 41 times the equivalent focus of the lens gives the required distance between lens and screen. In order to find the equivalent focus of a lens, it is con- venient, in the absence of special apparatus, to proceed as follows:—Focus upon a white surface an image of the Sun or other distant object, taking care to place the lens axis as nearly as possible in line with the object, and perpendicular to the surface receiving the image. When the image is sharply focussed, measure carefully the dis- tance between it and the nearest surface of the lens. Repeat this operation with the lens reversed, and measure the distance to the same surface as before; in this case, the surface furthest away. The average of the two measurements thus obtained is approximately the equivalent focus of the lens. I am indebted to Mr, Taylor, of Leicester, for the fol- lowing useful table:—