SAAO buys UK optics

South African observatory turns to the UK for high precision optics…
The South African Astrophysical Observatory (Cape Town, South Africa) has purchased a series of high precision optics from Optical Surfaces Ltd.

The optical components including an aspheric plate, concave spherical mirror, field flattener lens and fold flat form the key elements of a Schmidt camera system which will enable researchers to extend the capabilities of the observatory’s 1.88 metre telescope which surveys most areas of infrared and optical astronomy.

The camera to be supplied to the South African Astrophysical Observatory (SAAO) is an f1.4 folded Schmidt design to be used with a grating spectrograph working from 330nm to 900nm.

Made from special grade Zerodur, the collimator mirror is a 137 mm-diameter aspheric plate designed to depart from spherical by 120 microns of which 42 microns is concentrated in the last 2.5 mm of the diameter. To produce this rapid change of slope and up turned edge required a detailed knowledge of the polishing profile of tools of various stiffnesses. Forming part of the Schmidt camera optics a 186mm diameter spherical mirror (300 mm radius) was manufactured also from Zerodur and surface finished to a uniform lambda/80 rms.

In addition, Optical Surfaces have supplied an off-axis plano-convex field flattener lens that sits in front of the CCD`s and a specially shaped fold flat with a rectangular central hole to maximise light throughput and a cut-out to allow the cryostat tube to get as close to the focus as possible. Both these additional camera elements were manufactured from hi-grade silica, which offers excellent homogeneity and high optical throughput.

For over 40 years, Optical Surfaces has contributed high grade optics for astronomical research, and this is a good example.