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Handbook for motion picture and stereopticon operators (1908)

Page scan 00031 from Handbook for motion picture and stereopticon operators

Record Details:

Title:
Handbook for motion picture and stereopticon operators
Date:
1908
Publisher:
Washington, D.C. : The Knega Company, Inc.
Volume:
Handbook for motion picture and stereopticon operators
Leaf #:
00031
Language:
English
Subjects:
Motion Pictures, Motion Picture Technology
Collection:
Books
Format:
Books
Contributor:
Niles Essanay Silent Film Museum
Sponsor:
Media History Digital Library
Coordinator:
Media History Digital Library
Date Added:
May 02, 2025
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Operator's Handbook 25 Stops. Most photographic lenses are marked in " f " numbers, on what is known as the " U. S." system, that is, the aperture is expressed as a fraction of the equivalent focus. Now with a given lens a stop with an aperture of twice another has an opening four times the area, admitting four times the light, so that the exposure for the latter would be four times that through the former to get the same exposure. The converse is also true, that a negative twice as far from a given aperture requires four times the exposure, because the light on the plate or film in the second position is spread over four times the surface in the first position. A lens of 4-inch equivalent focus and with diaphragm stops having openings of \, \, \, and y1^ inch would have the stops marked /-8, /-16, /-32, jf-64, respectively, each being that fraction of the equivalent focus of the 4-inch lens to which they belong. However, makers usually mark stops between these so that each requires but twice the exposure of the one next larger. It will thus be seen that a ready means of judging of the working speed of different lenses is available, for a comparison of the " f " numbers gives the desired information. Some makers, however, have adopted a system of numbering which gives only the comparative exposures for the stops of that particular