Reflecting Telescope Optics I

Active optics in modern large optical telescopes

“…For these, the development of active optics control systems, which can operate in closed loop at time intervals of the order of one minute, will be essential. Telescopes with somewhat different applications of active optics include the Chinese LAMOST project (Su, Cui, Wang and Yao [1998]) and the hexapod telescope of the University of Bochum (see the overview given by Wilson [1999]). LAMOST is a 4 m meridian type Schmidt telescope with a thin reflecting aspheric corrector plate, where the optimum shape of this plate depends on the zenith distance.…”

“…Measurements at the equatorially mounted ESO 3.6 m telescope showed that the d 80 values due to low spatial frequency elastic aberrations were of the order of 0.5 arcsec largely independent of the sky position (Wilson [1999]). Since the design of the M1 support of a telescope with an altazimuth mounting like the NTT was significantly easier, it was estimated that the NTT 1 1 1 1 1 1 2 2 1 NTT 115 273 192 479 434 732 737 852 1034 VLT 16 38 42 66 68 102 107 119 143 Symmetry 3 1 7 4 8 2 0 5 3 Order 2 2 1 2 1 3 3 2 3 NTT 1131 1229 1383 1577 1779 1749 2050 2077 2366 VLT 160 176 192 221 246 246 272 289 With such a thickness the stresses, which arise if the mirror is unintentionally supported by three points only, are well below the tolerable limit.…”

“…But, under good seeing conditions of, say, Θ = 0.5 arcsec the active optics system should operate in closed loop. It has been shown that the optical quality of the NTT can then reach the specification of d 80 = 0.15 arcsec for an operation in the active mode (Wilson, Franza, Noethe and Andreoni [1991]). …”

Planckpre-launch status: Low Frequency Instrument optics

“…To improve the image quality, the design has been optimized by changing the conic constants, the radius of curvature, the distance between the mirrors, and the tilting of both mirrors, using the spillover level and the wave front error as optimization parameters (Dubruel et al 2000). The primary mirror is elliptical in shape (but nearly parabolic since the conic constant is about −0.9) as in aplanatic configurations (Wilson 1996), and the size of the rim is 1.9 × 1.5 m. The offset of the primary reflector, i.e., the distance between its center and its major axis, is 1.04 m, while the secondary reflector offset is 0.3 m. The secondary mirror is elliptical with a nearly circular rim about 1 m in diameter. The overall focal ratio, F # , equals 1.1, and the projected aperture is circular with a diameter of 1.5 m. The telescope field of view is ±5 • centered on the line of sight (LOS), which is tilted at about 3.7 • relative to the main reflector axis, and forms an angle of 85 • with the satellite spin axis, which is typically oriented in the anti-Sun direction during the survey (Dupac 2008).…”

Thermal model calculations of enclosures for millimeter wavelength radio telescopes

“…The amount of captured radiation can be manipulated to some extent and is small in the case when the telescope, the floor, and the walls have a high-reflective low-absorption finish. This decoupling was discussed by Bregman and Cassel1985] and is applied on the JCMT enclosure (zinc-coated inner surface), on the FCRAO 14-m telescope (aluminum foil), and on several optical telescope constructions [Wilson, 1999] …”