An experimental study of the photography, from the ground, of objects in the upper atmosphere shows that the results are improved by the use of long-focal-length lenses, high contrast film, and color filters chosen with regard to the relative spectral qualities of the object and the sky background. The most difficult problem was the photography of dark gray objects against a blue sky, and for these conditions a blue filter gave best results. For these same conditions, an increase in vertical range (altitude) was found to give a greater decrease in subject contrast than an equal increase in horizontal range. Of lesser difficulty was the photography of bright, white objects against a blue sky; and for these conditions a red filter gave best results. Data were obtained regarding the optimum spectral-reflectance characteristics of targets for special purposes. The required characteristics of the photographic emulsion were the subject of a detailed study. A high contrast, high speed panchromatic film, especially designed for this work, is described. Exposure and processing data for this film are given.
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