A study has been made of the variation in resolving power with magnification for telescopic systems used to view Foucault test objects of different inherent contrast. The study included the use of a form of the K.D.C. Apparatus. The results of the study indicate the existence of an optimum magnification that can be used to resolve Foucault test objects and that the optimum value of the magnification depends upon the inherent contrast of the test object. As the test object contrast decreases, the optimum amount of magnification decreases. For test objects having an inherent contrast of approximately 100 percent, an optimum amount of magnification was found to be approximately 70× for each 25.4 mm of aperture of the telescopic system under consideration. For objects of 10 percent inherent contrast, the optimum magnification was found to be approximately 30× for each 25.4 mm of aperture.
HOWARD S. COLEMAN, MADELINE F. COLEMAN, and SAMUEL W. HARDING, "The Influence of Magnification on Resolving Power of Telescopic Systems for Foucault Test Objects of Different Inherent Contrast," J. Opt. Soc. Am. 39, 771-772 (1949)