A chopping secondary mirror system is at present in use at ESO's 3.6m telescope for the cancellation of the sky- and telescope background emission and its variations. The chopper system achieves: - square wave and sawtooth chopping with amplitudes up to 10 arcmin and frequencies from 0-40 Hz, - stability of <1 arcsec ( <.2 on sky) in flat part of waveform, - risetime of about 6 msec, - flexure of <7.5 arcmin for any 30 degree tilt, - no vibrations induced in or transmitted to the rest of the mechanics (telescope). The chopper system is attached to a subsystem which enables the mirror to be rotated and focussed. The mechanics, optics and electronic control of the system are described and its performance is presented.
A. van Dijsseldonk,
A. F.M. Moorwood,
"Chopping Secondary Mirror For The ESO 3.6m Telescope", Proc. SPIE 0817, Optomechanical Systems Engineering, (1 January 1987); doi: 10.1117/12.967409; https://doi.org/10.1117/12.967409