International photographer (Jan-Dec 1935)

April, 1935 T h INTERNATIONAL PHOTOGRAPHER A inetcen shadowless lighting will require an increase in developing time of 50 per cent, or even greater. On the other hand subjects photographed in bright light casting pronounced shadows should be given a decreased developing time of 10 to 20 per cent. Photoflood and P'hotoflash lighting usually tends towards extreme contrast, which calls for about one-third reduction in the normal developing time. As it has been mentioned the above figures are approximate and intended as a guide in developing negatives of different subjects. The type of film used, and the exposure given are also factors which will determine the alteration necessary in the developing time ; and the photographer should bear in mind the increase in graininess with an increase in developing time, especially if a fine grain type of film is not employed. A little experience with the type of film, and developing formulas used is called for before the photographer can arrive at definite figures of the change necessary in the developing time, for different subjects. Green Filters: With summer rapidly approaching many workers will be considering the acquisition of additional filters to their equipment, and naturally the new green filters will be given thought. Some photographers are still puzzled about the manner in which such filters function, and why they are recommended as ideal for use with both orthochromatic and panchromatic films. The usual yellow filter we know holds back a portion of the blue and violet light, according to its depth, and so helps to overcome the excess sensitivity of the film to the shorter wave-lengths of light. Particularly do we feel the need of this service of the filter when we are photographing blue skies. Green filters also hold back blue light, and in addition some red light. For orthochromatic films they are suitable because of their retarding action on the blue light, the holding back of red light by the green filter is of no consequence in this case for orthochromatic films are not sensitive to red. The modern supersensitive film is usually too sensitive to red besides blue, and the green filters are suited for use with such films because they hold back a portion of the red light, besides the blue. In the selection of filters the number offered by the market may lead the amateur to think that to have a suitable set entails considerable expense and the necessity of carrying around about a dozen filters. However, the run of work covered by the average miniature camera photographer will By Augustus WOLFMAN not require more than three or four filters. Two yellow or green filters, of different density, and a light red filter such as the 23-A will be found to serve for practically all purposes. The Addition of Bromide to D-76: Eastman Kodak Company states that finer grain can be obtained with the popular D-76 formula by the addition of bromide. However, this is accomplished at the expense of loss of emulsion speed and increased time of development. An idea of the effect of bromide on the relative speed and the time of development can be had by referring to the table below, for which was used Panatomic film : Grains per Gal. Formula D-76 0 0.6 Low Contrast 8 min. 0.8 Normal Contrast 15 min. 1.0 Above Normal i lontrasts 25 min. Relative Speed 100 60 9 min. 16 min. 21 min. 75 150 15 min. 23 min. 40 min. 50 300 20 min. 30 min. 55 min. 25 It will be noticed that when 300 grains of bromide are added to a gallon of developer it is necessary to give as much as four times as great an exposure in the first place as when developing with D-76 without the additional bromide. It is suggested that workers who wish to try the use of additional bromide should add 60 grains to each gallon of developer. Mixing the Developer: At times the amateur may remove a processed film from the tank, notice that it is badly fogged, and wonder why. In many cases it is (Turn to Page 28) BACK GROUND PROJECTION STEREO — PROCESSING GEO, J. TEAGUE Rock — Steady Mitchell or Bell & Howell Registering COMPLETE RENTAL SERVICE General Service Studio Hollywood Equipment Europe &. Hollywood MACHINES MANUFACTURED Please mention The International Photographer when corresponding with advertisers.