Page:Journal of the Optical Society of America, volume 30, number 12.pdf/77

 national dispute has arisen out of the question whether the vitamin-deficient see “redder” than the well-fed people of America.

Developments in optical apparatus were found to be responsible for much of the progress during the last quarter-century. The controlled manufacture of ruled gratings, the discovery of supersonic gratings, the Schmidt camera, and aspheric lenses were given special mention.

Great advances in the measurement and specification of color have resulted from the development of photoelectric spectrophotometers and the concurrent development of a standard trilinear coordinate system. In the practical field, fluorescent lighting, photographic flash lamps, phototelegraphy, television, and the electron microscope are the most recent contributions of optics.

Advancement in science depends upon the perfection of the tools with which it works. Mr. Graeper assigned a large part of this responsibility in the optical industry to the methods of inspection employed by the optical instrument manufacturers.

Availability of materials, of course, is another factor in production, especially of those materials which are artificially producible. In this connection, the recent discovery of a deposit of a high quality calcite in one of our southwestern states is particularly interesting. The fact that methods of manufacture in the last twenty-five years have culminated in a perfection of manufacturing techniques which equal the best inspection methods, may be regarded as both a challenge to inspection methods and a tribute to the quality control in manufacture.

Dr. Mees began his talk by comparing the size and weight of the equipment needed by the photographer in 1900 to that which he carries in 1940. The most important developments in photography during the last twenty-five years have been brought about through the cooperative efforts of physicists and chemists, but they have been made commercially possible because of the increased popular interest in photography. The things the amateur wanted were pictures easier to make, pictures in motion, and pictures in color. The technical developments which have fulfilled these wishes are: (1) improved methods of the optical sensitizing of emulsions; (2) the development of mechanized reversal processing; (3) the introduction of elaborate miniature cameras of high mechanical quality; and (4) the introduction of the integral tripack systems of color photography.

The improved methods of optical sensitizing arose from the development of the polymethine dyes, in which two nuclei are connected by a chain of methine groups. The absorption and sensitizing spectra of these dyes depend upon the length of the chain and the weight of the nuclei. The new dyes increase the sensitivity of slow, fine-grain emulsions more than they do that of high speed emulsions; and this makes it possible to prepare films of satisfactory speed having an image structure which allows a considerable degree of enlargement. This development has greatly encouraged the use of miniature cameras.

The growth of amateur cinematography has been dependent upon the excellent results obtained by reversal processing carried out on conntinuous developing machines using automatic compensation for the second exposure.

On the optical side, the growth of amateur cinematography and of miniature cameras has led to the introduction of lenses of very much higher aperture than those used previously, and this has been assisted by the introduction of improved glasses, particularly glasses of low dispersion and high refractive index.

The use of the integral tripack has been very successful in color photography, and the majority of all substandard motion pictures are now made in color. In other branches of photography, the use of color processes is constantly increasing.

To make things disappear was once a conjuror’s trick, but Dr. Cartwright demonstrated for his audience that optical advancement has made this magic possible without legerdemain. Glass is visible because of the light it reflects; it becomes invisible when it is sufficiently transparent.

H. Dennis Taylor in 1892 observed that camera lenses were “faster” after they became tarnished. Several methods for artificially tarnishing glass were subsequently developed. A more physical approach to the problem was made in 1936 by J. Strong, who evaporated films