1. Analogical problems have been solved among others byL. C. Martin: An Introduction to Applied Optics, 1930, Vol. I, 123–126; D. D.Maksutov: Astronomicheskaya optika, 1946, 19–28; H. H.Hopkins: The Photographic Journal, 86B (1946), 73–84.
2. L. E. Jewell: Journ. Opt. Soc. Amer., 2–3 (1919), 51–61; Kodak Scient. Abridged Publ., 77 (1919).
3. S. Huber: Zs. f. Instrkde, 63 (1943), 333–341, 369 to 383.
4. G. Hansen: Zeiss Nachrichten, 4 (1942), 129–137.