We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.
Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.
498
WADDELL
November
design features found to be desirable from that standpoint are identical with those above for good design of cameras.
In order to show how the above design objectives are achieved, it will be desirable first to consider the matter of maximum angle of incidence i to be used. In this connection, reference is made to Fig. 2, a plot of velocities of displacement computed from (5) for various values of incidence angle i. It is to be noted that the velocity of the image is maximum at 0 angle and decreases rapidly as the angle increases. By proper choice of gearing for driving the prism the image
can be kept in step with the film within approximately 2 per cent for angles from 0 to 10 degrees and hence a maximum angle of incidence of 10 degrees is a logical value. The angle can be limited to this value by choice of apertures before and in back of the prism. In this connection it is of interest to note that the cone of light from an //2 lens having a 2inch focal length subtends an angle of approximately 30 degrees when the object is at infinity. If no ray in the cone is to strike the prism at an angle of incidence of more than 10 degrees at any time in the rotation of the prism the useful angle subtended by the lens is only about 10 degrees.
Having selected the prism glass for maximum index of refraction and having chosen the maximum angle of incidence the next and final step in the prism design is to determine its thickness. This involves the use of (4). It is first necessary, however, to establish the value of ss'.
It is obvious from .Fig. 1 that ss' is the distance a specific point of the image moves during the exposure of the corresponding point on the film. • It is equally obvious that exposure of the entire scene to the film (within one picture frame) does not occur simultaneously but proceeds lengthwise on the film as the prism rotates. Having
RELATIVE VELOCITY
TROM EQUATION 5
^
N
60
\
N
\
\
\
0* IO* 20* 3O* 40* 5<
I
Fig. 2