Resolution Tester

an instrument for measuring the resolving power of photographic materials. In projection resolution testers—the most common type—a reduced image of a hatched optical test pattern is projected on the photographic material through a microscope objective with a reversed light beam, usually with a U-shaped brightness distribution along the grid. A series of such images, which are obtained with different precisely controlled exposures, creates a resolution chart on the photographic material; the resolution of the material and its dependence on exposure are determined by examining the field of the resolution chart under a microscope. The value of the resolution thus measured is a function of the objective’s aperture and is highest with apertures of about 0.2 to 0.3; the objectives of projection resolution testers consequently have definite apertures.

The photographic contrast of the images of an optical test pattern is reduced in projection resolution testers as the density of the strokes is increased. On the other hand, in the interference resolution testers that are used for studying materials having very high resolutions—for example, those used in holography—the contrast does not depend on the density of the interference bands imprinted on the photosensitive layers; the brightness of the bands varies sinusoidally along the grating. The spatial density of the bands can be varied by shifting the optical parts that create the interference pattern of the interferometer.