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Feb., 1930] ABSTRACTS 261
and limitation to normal speeds. Brusten's apparatus is mounted on a counterbalanced lever on a movable stand. Pictures can be made from almost any angle and speeds up to 100 per second are possible.
Goal of Photographic Optics. A. SONNEFELD. Phot. Korr. 64, 1928, p. 376. Because of light losses due to reflection and absorption, the useful limit of aperture has been reached with lenses of ordinary types of f/2 to //1. 5. Such lenses, however, have the defect of not being perfectly zonally corrected. Nonspherical refracting surfaces (Abbe surfaces) might remove the defect and result in fewer components and less light absorption.
New Actinometer. Luminous Source of Constant Spectral Composition. R. LANDAU. S. & J. P. Inf. Cine., 8, 1928, p, 131; 9, 1929, p. 5. An image of the subject is formed on a phosphorescent screen. A mirror placed clear of the objective axis is inclined so that light received from the surface is reflected in a direction parallel to that of the light from the objective. This light consists of polychromatic reflected light and monochromatic light due to phosphorescence. A shutter is so placed that it will allow the light from the objective to reach the screen but will intercept the reflected image light from the mirror. The shutter will allow the phosphorescent light to pass intermittently. The phosphorescent light is of constant spectral composition and is proportional to the actinic light in the image. The phosphorescent image light may be inspected with a photo-cell.