Abstract

A method for making precise resolving power measurements has been developed. This method makes it possible to take into account the ill effects of stray light as well as the common optical aberrations. The method utilizes a device referred to as “The Kinetic Definition Chart Apparatus” (hereafter abbreviated to K.D.C. apparatus). The K.D.C. apparatus provides a means of continuously varying the angular subtense of the markings of a test object without changing the apparent distance between the test object and the optical device under test. Provision is made to vary the contrast and the brightness level of the test object. In order to simulate natural conditions, the test object is surrounded by a region, referred to as “the artificial sky,” which may be illuminated to any desired brightness level. The Artificial Sky fixes the brightness level at which the observer’s eye is adapted, and provides a means of determining the ill effects on resolution caused by stray light that would normally be present in the optical device under consideration. Fixtures have been made which make it possible to measure the resolution at various field angles for an optical device under test. By means of auxiliary magnification, it is possible to test an optical device at full aperture and practically to eliminate differences among observers by reducing the diameter of the pupil of the observer’s eye to less than 1 mm. For comparison purposes, a high grade telescope, referred to as “the standard telescope” is used. The standard telescope is practically free from aberrations and stray light and has practically no loss in light transmission. This telescope provides a means of acquainting an observer with an image of high quality and resolves 4.51 seconds for each inch of aperture. A quantity, referred to as “the K.D.C. efficiency,” is introduced to describe the performance and the quality of optical devices. The K.D.C. efficiency may assume two different forms depending upon the end use of the data. In predicting the performance of an optical device, such as the telescope, K.D.C. efficiency is a measure of how much farther a given object is visible using the instrument than with the unaided eye. In the case of quality control of optical devices being mass produced, it is convenient to compare the limiting distance of resolution of the device under test with that of the standard telescope having the same entrance pupil as the instrument under test. The two definitions of K.D.C. efficiency are equivalent if the diameter of the pupil of the eye being used in the observations is less than 1 mm. The method described above has been used to determine the performance and quality of telescopic systems, photographic systems, eyepieces, and microscope objectives, and to measure the resolving power of the human eye under a variety of conditions.

© 1947 Optical Society of America

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