The American annual of photography . al dark-ness or in a certain green light which emitted rays betweenabout 5100 A. U. and 5400 A. U. This is in the blue-green re-gion of the spectrum and is the so called safe light, but it takessome time for the eye to become accustomed to it as it isvery weak. But even this safe light will soon cause fogwith some emulsion, so it must be used with care. The reasonfor the comparative insensitiveness of panchromatic emulsionsto this region of the spectrum is that the majority of the pan-chromatic sensitizers in use show but little absorption for thiscolor, an
The American annual of photography . al dark-ness or in a certain green light which emitted rays betweenabout 5100 A. U. and 5400 A. U. This is in the blue-green re-gion of the spectrum and is the so called safe light, but it takessome time for the eye to become accustomed to it as it isvery weak. But even this safe light will soon cause fogwith some emulsion, so it must be used with care. The reasonfor the comparative insensitiveness of panchromatic emulsionsto this region of the spectrum is that the majority of the pan-chromatic sensitizers in use show but little absorption for thiscolor, and so an insufficient amount of light is transmitted toeffect the emulsion. But this was not Dr. Lueppo-Cramers first work alongthese lines. He had noticed as early as 1901 that the sensitive-ness of plates was greatly reduced when in certain developers,especially those belonging to the paramidophenol class. Platescould be developed in these developers in a light so brightthat when hydrochinone was substituted they were hopelessly 96. fogged. Later Dr. Lueppo-Cramer found that aqueous solu-tions of certain developing agents had a similar but far strongeraction in reducing the sensitiveness. At the present timediamidophenol hydrochloride (Amidol) and triamidobenzolhydrochloride are the only substances possessing this propertyto a practical degree that are not dye stuffs. The most effective was a per cent, solution of Amidolin distilled water without any other admixture. The plateafter exposure was placed in the above solution for one minutein darkness and then developed with one of the usual de-velopers excepting glycine which caused a dichroic fog. An-other plate having the same exposure but not treated wasplaced in the developer at the same time and both developedin bright yellow light. The plate which had not been treatedbecame badly fogged, while the other remained clear. Ortho-chromatic plates showed but little difference between thetreated and untreated plates; they bo
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Keywords: ., bookcentury1900, bookdecade1920, bookpublishernewyo, bookyear1922
