Background and first results from the new AAO/UKST H survey

The high quality H interference filter

As no suitable AAO H filter was currently available a vendor (Barr Associates) was identified to supply a high specification, large monolithic interference filter for use at the UKST's focal surface. Very stringent optical tolerances were necessary as the filter was to be used in the converging f/2.48 beam and the excellent imaging capabilities of Tech Pan must not be compromised. Details of the specifications achieved are given in Parker & Bland-Hawthorn (these proceedings). This interference filter, probably the largest of its type in astronomy, has a multi-layer di-electric stack with a `circular aperture' of 305 mm diameter coated on to the mm RG610 glass substrate. This permits a field of about 5.5 degrees diameter to be observed in H. The CSIRO National Measurement Laboratory in Sydney have quantitatively confirmed that the filter meets the stringent optical specifications set, especially the 70 Å FWHM filter bandwidth and 6590 Å central wavelength in collimated light.

The exceptional optical quality of the filter has been demonstrated on the telescope by the first 2 hour H exposures taken in good seeing during April 1997. These preliminary exposures exhibit excellent imaging and uniformity across the entire field. They also confirm the 305 mm diameter clear aperture of excellent H sensitivity of about 5.5 degrees on the sky.

© Copyright Astronomical Society of Australia 1997