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2. Chelt’sov, W. S., Jordanski, A. N., Bongard, S. A. and Katchenko,T. G., Proceedings of the International Conference for Scientific Photography Köln, 1956 Verlag Dr. Othmar Helwich, Darmstadt 1958, p.485.
3. Mees, C. E. K. and James, T. H. “The Theory of the Photographic Process,” Macmillan, New York 1966, p.333.