Wf

f/5

sideros.

Schmidt

Abbreviations: PH: paraboloid-hyperboloid, WF: wide field, RC: Ritchey-Chretien, 4M: 4-mirror design, PE: paraboloid-ellipsoid, Ne: Newton, Ca: Cassegrain, Co: coude or recombined, Pr: prime, Na: Nasmyth, Gr: Gregory, W: Wolter grazing system, Fi: final image focus after i grazing-incidence mirrors.

The sign = in column two stands for equivalent aperture diameter.

• John D. Strong (1905-1992) developed the evaporation process of aluminizing glass mirrors under vacuum [150]. This required a vacuum tank, efficient pumps, and tungsten heaters for the aluminum sublimation at 1,460 K. For large mirror reflective coatings, this technique definitively replaced the silver-on-glass chemical method after 1935.

• Mark U. Serrurier (1905-1988) invented the compensated flexure tube for the Palomar 5-m telescope. This allows maintaining perfect alignment between the primary and secondary mirrors, thus preventing primary coma de-centering aberrations. He noticed that when the declination axis is fixed on a rigid hub defining the center of the telescope tube, both the bottom ring supporting the primary mirror and the head ring supporting the prime focus cage or the Cassegrain mirror can flex by the same amount if they stay in parallel planes. He found the solution with triangular struts from the hub to each end by deriving the appropriate section ratio between the upper and lower bars. This is known as Serrurier's truss [145] and is directly applied, or used as a basic concept, in all designs of large telescope trusses.

• James G. Baker (1914-2005) invented several forms of wide field telescopes that were built in large numbers for ground-based and space astronomy. Among them, one may cite the flat-field Baker-Schmidt-Cassegrain telescopes [170], the flat-field Paul-Baker three-mirror telescopes and, in 1945, the Super-Schmidt cameras and the Baker-Nunn satellite tracking cameras [8]. Baker was probably the first person to use a computer in optical design.

• Norman J. Rumsey (1922-2007) discovered, in 1969 [137], a flat- and wide-field three-mirror telescope presenting particularly interesting features. His reflector, with three hyperboloid surfaces, is an anastigmat which is four-times shorter than the equivalent Schmidt. Furthermore, the de-centering problems of the primary and tertiary mirrors are avoided by figuring these mirrors in the same blank. Sky surveys with detector arrays would benefit from the high quality imaging. Modified-Rumsey telescopes with the primary and tertiary mirrors - designed as a continuous optical surface on a single substrate - can be simultaneously aspherized by active optics methods (cf. Chap. 6).

• Daniel Malacara, in 1978, edited Optical Shop Testing [101] which describes all tests applicable to optical components and systems. This book had become a classic of optical shops. In collaboration with specialists in the field, the book is a review on mountings using interferometers, Foucault, Ronchi and Hartmann tests including the phase modulation tests (Zernike, Lyot, etc.), tests on a star, holographic test, fringe scanning technique, and many useful null testing configurations for compensating the aberrations of the most-common wavefront surfaces.

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