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

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

Aug 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998spie.3352..328p&link_type=abstract

Proc. SPIE Vol. 3352, p. 328-333, Advanced Technology Optical/IR Telescopes VI, Larry M. Stepp; Ed.

Computer Science

3

Scientific paper

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.

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