SAAO - South African Astronomical Observatory

The Spectrograph



Cassegrain Interface Unit

Fibre Optic Feed

A pair of 16 metre long Polymicro step index optical fibres relays star and arc/flat-field light from the telescope to the spectrograph. The fibres are of the UV-enhanced, high tex2html_wrap_inline495 (i.e. `wet'), variety with a pure silica core of 50 µ m diameter (see the specifications).

At the telescope end, the fibres are separately mounted in standard SMA fibre connectors. One of these is screwed into a conical mounting flange which connects to a Melles-Griot fibre positioner. This fibre is fed by starlight by re-imaging the entrance aperture onto the fibre core. The other fibre is plugged into a similar unit (at 90° to the star fibre), into which background sky is fed. A moveable mirror can be inserted which directs either an arc or flat field into one or both fibres.