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A technique was worked out for making Fresnel off-axis parabolic mirrors by selective deposition of evaporated aluminum onto spherical mirrors. Tests were made to determine the extent and the nature of the interference between the light reflected from the different zones. When the illuminating slit was parallel to the principal radius there was no undesirable interference and no appreciable reduction in resolving power.
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L. G. Schulz (1947) studied this question.
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