The design and construction of a spectrograph and the investigation of the spectral sensitivity of various photographic emulsions
Caudron, Jarvice G
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The spectral sensitivity of five film types was measured over a region of 3380 to 6000 Angstroms. Curves of sensitivity vs wave length were produced for each film. The method of producing these curves was to expose the film to the continuous spectrum in the spectrograph, develope and make a microdensitometer trace in order to secure a density vs wave length curve. From this curve densities at various specified wave lengths were obtained. Using the Eastman IB sensitometer H and D curves were obtained throughout the wave length interval of interest. From these curves a difference in exposure, Δlog Hλ, is obtained: Δlog Hλ= log HD - log Hλ where log HD is the irradiance required to give a density of 1.00 and Hλ the irradiance of the same wave length in the spectrograph. The spectral radiancy ratio Rλ/Rλmax obtained from the black body radiation curve for the source is corrected by the Δlog Hλ value log H = Δlog Hλ + log Rλ/Rλmax The spectral sensitivity S, is the reciprocal of H. A special spectrograph was designed and built for this work. It was designed to use a concave grating so that glass elements would not interfere with wave lengths below the 4000 Angstrom point. The film was scanned in a recording densitometer to give a trace of density vs wave length. The H and D curves for the various wave lengths of interest were obtained on an Eastman IB sensitometer. The Wratten 78AA conversion filter was replaced by narrow band interference filters. The sensitometric strips made on the sensitometer were read on an Ansco-Macbeth densitometer. The five films under consideration were Eastman Tri X and Panatomic X, Ansco 569 and D 643A, and Illford BY 2670. All films were processed in Eastman D-19 developer at 68° Fahrenheit using standard processing procedures.
Thesis (M.A.)--Boston University