Fast tip-tilt secondary for the Blanco 4-m Telescope

Gabriel Perez; Richard Elston

doi:10.1117/12.319320

25 August 1998 Fast tip-tilt secondary for the Blanco 4-m Telescope

Gabriel Perez, Richard Elston

Proceedings Volume 3352, Advanced Technology Optical/IR Telescopes VI; (1998) https://doi.org/10.1117/12.319320
Event: Astronomical Telescopes and Instrumentation, 1998, Kona, HI, United States

Abstract

A very low cost fast tip-tilt secondary mirror has been implemented on the NOAO Blanco 4m Telescope located on Cerro Tololo, Chile. The secondary mirror is an 800-mm diameter Cervit mirror, lightweighted to 92 kg and polished to match the optical quality of the existing 4.0-m primary. The final focal ratio is 14.5. The secondary mirror is mounted in a cell which provided high torsional inertia and stiffness. This mirror cell drew heavily from an existing secondary mirror cell, which had been built for the Blanco Telescope many years ago but never used. Modifying an existing mirror cell provided significant cost savings. The mirror is axially attached to this cell via three piezo electric actuators, which are computer driven to provide the tip-tilt corrections required. A mercury band provides radial support. Unlike most tip-tilt systems, this secondary is not momentum compensated. Tests have shown that the telescope is unaffected by the reaction forces induced by motion of the secondary mirror. Eliminating the momentum compensating system makes the mechanical design simple, reliable and inexpensive. The system will normally operate at frequencies in the range of 10 to 40 Hz with only very small amplitudes at the higher frequencies. When operated as part of a closed loop feedback system using a fast CCD camera operating at 240 Hz the RMS image motion of stars is reduced to 0.02 arcseconds. All image motion at frequencies lower than 25 - 30 Hz is removed.

Citation Download Citation

Gabriel Perez and Richard Elston "Fast tip-tilt secondary for the Blanco 4-m Telescope", Proc. SPIE 3352, Advanced Technology Optical/IR Telescopes VI, (25 August 1998); https://doi.org/10.1117/12.319320

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