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.
THE FILM 81
the trade name for the camera lens of 1.000-in. major diameter of mounting thread). Thai standard specifies that ". . . all registration distances shall be measured from the lens scat to the center of the picture aperture in the film plane." As will be pointed out later, errors in registration distance of 0.002 to 0.007 in. are quite common; since the error is usually made in the "full" direction, it may be corrected by milling off the appropriate amount of metal from the lens shoulder. Back* has suggested a relatively simple arrangement that can be constructed by a person with some training in physics. This apparatus, which checks absolute transmission, is an embodiment of the concepts of Berlant, Gardner, and others. If the reference apparatus is too costly or too complicated for the individual photographer, it is possible to have a reference lens measured at a commercial testing laboratory on some apparatus like that which Back suggested, and to make comparisons among the lenses at hand using the tested lens as a reference. Such organizations as Electrical Testing Laboratories have the necessary "knoAY-how," and the charges for their services are very small indeed in terms of the services rendered.
Exposure Tests
When using lenses for making comparative exposure tests, the identical group of lens // stop and focus settings should be used in all cases. These should be carefully and accurately set to clearly defined markings in the recommended series of values. If such markings do not exist, it will pay to have them engraved. The lens should be returned to its manufacturer for this work.
The Film
Last but not least in importance is the film itself. As pointed out in Chapter 2, no two lots of manufactured film are sufficiently alike to permit indiscriminate interchangeability in use. As a practical matter, the variations in base characteristics are usually of little importance ; it is the variations of sensitometric characteristics that require attention.
A convenient starting point is to provide sufficient film of the same emulsion-lot number for the complete production picture. Obviously, in an estimate of the film required, due allowance must be made for retakes and exposure tests. Every manufacturer of motion-picture film keeps complete and accurate data concerning the sensitometric charac
* JSMPE, 49. (Aug. 1947) — several papers including that of Back.