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.
not of importance except in a few cases. Practically all commercially available emulsions can be made with properties of high constancy, but in a few rare cases variations may occur. Intentional emulsion changes are carefully called to the attention of consumers by manufacturers if the changes are of a nature which cause inferior results when not regarded in use. It is a common practice of at least one manufacturer to notify the tiade of changes by the use of stickers placed on the film container.
Most manufacturers recommend that development be conducted as soon after exposure as possible, but it is not exceptional for excellent results to be obtained on negatives developed several months after exposure. On the other hand, emulsions have been known to lose 50 per cent of their latent image within a few days, and so it is best as a general rule to develop negatives as shortly after exposure as possible.
Purpose Factors
The relation of the speed rating of a film to the use for which the film is intended is a consideration not often sensed by the man in practice. A certain manufacturer received a number of letters asking why a well-known emulsion in cut film form was rated by the manufacturer one-half stop slower than the same emulsion on roll film. The answer, of course, becomes obvious when it is recalled that amateur negatives are for the most part better suited for the purpose when less dense than negatives usually desired by the professional photographer. Negatives to be used for contact printing are often denser than those intended for projection print
ing. Portrait negatives in the majority of cases are less dense and softer in contrast than commercial type negatives. In some special cases, such as negatives of black-and-white-line originals, exposures are made for the highest densities, whereas in ordinary negative-making of continuous tone subjects, much lower density levels are used. Many other instances could be given where the exposure given a film depends greatly upon the purpose for which the negative is being made. For a system of speed numbers to be valid for all negative purposes is not comprehensible.
Illumination Factors
Every photographer well knows that a flat ly lighted subject allows much more variation in exposure than a subject with contrasty lighting. Although recently disputed by a popular photographic writer, it is a good practice in nearly all cases to expose for the deepest shadows in which detail is desired. When the subject is strongly lighted, this means that the exposure required to obtain shadow detail will place the highlights very high on the D-Log E curve. If the highlight densities are too high, they become “blocked-up” and cannot be printed: therefore exposure in such cases is very critical. Contrasty lightings also produce negatives of such high contrast, if developed normally, that no paper is soft enough to allow the making of good prints. This is often overcome by a lower degree of development, which in turn decreases film speed and necessitates longer negative exposure than conditions might indicate.
The character of the light source has been considered in reference to its
16