Active optics
The active optics are used in reflector telescopes to compensate for the mirror curvature that occurs when the telescope is pivoted.
In astronomy , mirror telescopes are built with ever larger main mirrors in order to increase the light-collecting effect and the resolution . Glass ceramics (e.g. Zerodur from Schott AG, Mainz) are mainly used here, as they have a very low coefficient of thermal expansion . For weight reasons, the mirrors are made as thin as possible. As a result, however, they lose their rigidity, and when pivoting they bend under their own weight, which causes aberrations .
In order to correct these imaging errors, the mirrors are mounted on actuators . A control unit compares the actual and target geometry of the mirror and the actuators can be used to compensate for any deformation of the mirror.
Active optics were first used in the ESO's New Technology Telescope in 1989 , followed by Keck-1 in 1992 . The four telescopes of the Very Large Telescope (VLT), the Large Binocular Telescope (LBT) and the Gran Telescopio Canarias also use this technique.
While the active optics compensate for slow mechanical influences of the telescope, the adaptive optics reduce the rapidly changing disturbing influences of the atmosphere. The wavefront is typically measured with a Shack-Hartmann sensor and then with active optics the main mirror, with adaptive optics a smaller auxiliary mirror is bent in the beam path for error correction. In the case of slow active optics, the actuators are typically motorized or hydraulically adjustable support points. In contrast, piezo actuators or voice coil actuators are typically used with the much faster adaptive optics .
literature
- MD Rhodes: Thermal active optics technique for correcting symmetrical distortions in space telescope mirrors. NASA Langley Research Center, 1970, abstract , pdf NASA Technical Reports Server, accessed July 7, 2016
- John W. Hardy: Active optics - A new technology for the control of light. IEEE, Proceedings, Vol. 66, June 1978, pp. 651-697, bibcode : 1978IEEEP..66..651H , pdf @ dtic.mil, accessed July 7, 2016
- William J. Cuneo: Active Optical Devices and Applications. Proceedings of the Society of Photo-Optical Instrumentation Engineers, April, 1980, Washington, DC, bibcode : 1980SPIE..228 ..... C , pdf @ dtic.mil, accessed July 7, 2016
- Raymond N. Wilson : Reflecting Telescope Optics I , Springer-Verlag Berlin Heidelberg, 2nd ed. 2004, corr. reprint 2007, ISBN 978-3-540-76581-3 , doi : 10.1007 / 978-3-540-76581-3
- Raymond N. Wilson : Reflecting Telescope Optics II , Springer-Verlag Berlin Heidelberg, 1999, ISBN 978-3-642-08223-8 , doi : 10.1007 / 978-3-662-08488-5
- Gérard R. Lemaitre: Astronomical optics and elasticity theory Springer, Berlin 2009, ISBN 978-3-540-68904-1 , doi : 10.1007 / 978-3-540-68905-8
Web links
- Article about Active Optics at ESO (English; PDF file; 1.80 MB)
Individual evidence
- ^ Basic Principles of Active and Adaptive Optics. Pp. 223-226 in: Jingquan Cheng: The principles of astronomical telescope design. Springer, New York 2009, ISBN 978-0-387-88790-6 , @ google books