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.
294 HANDBOOK OF PROJECTION FOR
the screen center be much less than if the projection distance he long.
The Society of Motion Picture Engineers has set its seal of approval on the following:
"PROJECTION ANGLE.— The maximum permissible angle of projection shall not exceed twelve degrees (12°) from a perpendicular to the screen surface."
While this is somewhat ambiguous, we may, we think, accept it as meaning that the maximum permissible angle of projection shall not exceed twelve (12) degrees from a horizontal line passing through the center of the screen, when the screen sets perpendicular.
An angle of 12 degrees amounts, roughly, to 2.55 inches to the foot. By "roughly" we mean that is close enough for practical purposes, though it may be a very small fraction of an inch more or less. From the foregoing we readily see that if we
Multiply the proposed projection distance, in feet, by 2.55 and divide the result thus obtained by 12, the final result will be the height, in feet, the lens may be above the screen center without exceeding a 12 degree angle of projection.
By subtracting the distance of the projection lens from the floor of the projection room from the result obtained by the application of the above rule we shall have the maximum permissible height of the projection room floor above the screen center. See remarks concerning 12 degree angle. Page 255.
In considering possible available projection room locations the angle of projection, and consequent distortion are, of course, of first importance, though this consideration is rivaled by another, namely,
LIMITS OF VIEW. — Select any familiar object, such as, for instance, a tree. Carefully observe it, in normal light, at a distance of 150 feet. You will of course see the tree as a whole quite plainly. You may even see most of its individual leaves, though in some places, unless your eyes are above the average, they will appear mostly as green masses of foliage, with the outline of individual leaves difficult to trace. Advance to a one hundred foot distance. You can now perhaps distinguish the outline of all the leaves, but the trunk most likely will only show as a light or dark object, without much detail of the bark being visible. Advance to seventyfive feet and see how much more clearly you are able to