next up previous contents
Next: Fibres Up: Status (Nov. 1994) Previous: Status (Nov. 1994)


AF2 underwent a rigorous test programme in Durham and Cambridge prior to its shipment to La Palma. There it was commissioned on the telescope in a ten-night run in October, 1994. Although hampered by bad weather, the run demonstrated performance levels comparable with those achieved in the UK tests.

Absolute placement accuracy is 15 microns (0.25 arcsec) with a mean placement time of 10 sec per fibre, the maximum number of permitted iterations being five. Full field set-ups took 20 to 25 minutes.

The emphasis of the commissioning tests was to establish the exact transformation required between sky positions and AF2 (x,y) coordinates so that each fibre can be precisely placed on its target. This involves knowledge of the geometry of the prime-focus field as imaged through the corrector. Initially, the information was determined from measurements of prime-focus plates. To refine the transformation as it applies to AF2, the robot itself was used to measure the positions of stars in the field. It can do this very accurately with the two sky-viewing probes. Towards the end of the run this mapping process was providing a fit with rms residuals of only 0.35 arcsec.

It was also demonstrated that field acquisition was straightforward and could be done in under a minute.

AF2 performed reliably throughout the run and all aspects of its operation were tested. The daytime jobs of putting it on and taking it off the telescope are quite complex procedures. They went relatively smoothly, however, and no particular difficulties are foreseen in carrying them out routinely. Remaining work on AF2 consists mainly of tidying up a few loose ends in both hardware and software. The instrument will be formally handed over when WYFFOS is commissioned.

Tue Aug 15 16:42:46 BST 1995