Journal of the Society of Motion Picture Engineers (1930-1949)

Page scan 000372 from Journal of the Society of Motion Picture Engineers

Record Details:

Title:
Journal of the Society of Motion Picture Engineers
Date:
1930-1949
Publisher:
New York, N.Y. : The Society
Volume:
Journal of the Society of Motion Picture Engineers
Leaf #:
000372
Language:
English
Collection:
Technical Journals
Format:
Periodicals
Contributor:
Prelinger Library
Sponsor:
MSN
Coordinator:
Media History Digital Library
Description:
The Journal of the Society of Motion Picture Engineers (SMPE)Êdocuments the technological progress of the film industry, highlighting technical developments in production and exhibition. Of special interest are articles about special effects, theater practices, lighting, and the introduction of the 16mm format. Initially titled "Transactions of the Journal of the Society of Motion Picture Engineers."Digitized by the Prelinger Library and the Library of Congress Motion Picture, Broadcasting and Recorded Sound Division.
Date Added:
July 19, 2022
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LENS-CALIBRATION REPORT 369 Equation (1) shows that for a very distant object of brightness B, the image illumination at the center of the field is proportional to tA/f2. For a circular aperture, (3) shows that the central image illumination is proportional to £/(/ number).2 Note also that in (4), the sine is correct and not the tangent, because in a lens satisfying the sine condition the "principal plane" is actually a sphere centered about the focal point. III. DEFINITION OF / NUMBER The definition of /number given in (4) above is in accordance with American Standard Z38. 4. 20-1948, paragraph 2.5. For a lens satisfying the sine condition and having a circular aperture, the / number r > _j L ' , ) | s z J : Fig. 1 is also equal to the ratio of the focal length to the diameter of the entrance pupil, thus 1 / number = : 2 sin 6' (5) If the lens aperture is noncircular, as often happens when an iris diaphragm is partly closed, the area A of the entrance pupil must be measured instead of its diameter D. The effective diameter D' of the entrance pupil will then be defined as lence, /number = !!_/./£. ^ (7) IV. DEFINITION OF T NUMBER In order to embody the lens transmittance and the area of the diairagm into a single figure which can be engraved on the lens, it is >posed to adopt a new term to be known as the "T number" of a