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A microphotometer of new design has been constructed with careful attention to rigidity of mounting and reliability of measurements. The light from a straight filament lamp is condensed on a fore-slit by an f : 1.5 lens without cemented combinations. The fore-slit is imaged on the spectrum plate by a lens combination having an effective aperture of f : 0.75. To avoid further lens losses, a shadow projection on a barrier layer photo-cell is used. The rigidity and precision of adjustment necessary for the use of lenses of such extreme aperture is provided by mounting the optics in an internally threaded brass tube, which is secured to the massive base by a flange, while the spectrum plate is clamped in a suitable frame, mounted on accurate slides. A motor-drive, engaging through a pedal operated clutch, provides a constant speed of traverse, independent of operator technique. A novel method is used for viewing the part of the spectrum under investigation. The wide aperture optical system transmits sufficient light to permit the use of a critically damped galvanometer, with a period of one and one-third seconds. At operating speeds which permit the maximum deflection to be observed accurately, no appreciable galvanometer lag is experienced. Readings of the opacities of five or six preselected lines may be made in one minute, with an error not exceeding one percent. The instrument has the speed and accuracy needed for routine production control work by quantitative spectrographic analysis.
© 1937 Optical Society of America
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