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Panchromatic Negative Film — Jones & Crahtree 169
panchromatic film must be used. Standard panchromatic negative fihn may be hypersensitized by treating with ammonia. The fihn is bathed 1.5 minutes in 4 per cent ammonia at 50°F and dried as rapidly as possible. Hypersensitized film does not keep for a very long time but can be relied upon for a week or more. The general sensitivity of the film is increased appreciably by this treatment but the green and especially the red sensitivity is increased in much greater proportion than the blue. The red sensitivity of film hypersensitized in this manner is about four times as. great as the standard product. A spectrogram showing quanlitatively the spectral sensitivity of hypersensitized panchromatic film is shown at B in Fig. 23. Even greater haze cutting can be obtained by using Eastman Panchromatic K film which is very sensitive to infra-red radiation (see Fig. 23, C) and not at all sensitive to the green, yellow, and orange of the visible spectrum. Any filter which completely absorbs the short wave-lengths to which the film is sensitive (wave-lengths less than 500 m/i) is satisfactory for use with the film. The photographs shown in Fig. 24 illustrate the haze elimination obtained by use of Panchromatic K film. Moonlight Effects. Some years ago, Prof. R. W. Wood of Johns Hopkins University called attention to the fact that landscapes when photographed by infra-red light present very peculiar and weird appearances. This is due to the fact that the light from the sky contains no infra-red radiation and hence the sky is rendered as totally black, while green foliage is rendered as white. This follows as a consequence of the pecuUar spectral reflecting characteristics of green leaves containing the coloring matter known as chlorophyll. Chlorophyll reflects quite strongly the extreme red and infra-red radiation. Hence in a photograph taken by infra-red radiation green leaves are rendered as white. In a paper pubUshed in No. 22 of these Transactions (p. 20) Mr. J. A. Ball suggested the use of film sensitized with Kryptocyanine for obtaining moonlight and night effects without the aid of artificial hght. Film of this type is now commercially available under the name of Eastman Panchromatic K. In Fig. 23 at C the spectrogram given shows quaUtatively the spectral sensitivity of this material. It will be noted that in addition to the usual sensitivity of ordinary film in the blue region it shows a band of high sensitivity having a maximum at wave-length 760 mji. This being in the infra-red region the eye is entirely insensitive to radiation of this wave-length. Panchromatic K film, as shown by the spectrogram, is insensitive to the green, yellow, and orange of the visible spectrum.