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Special Purpose Filters

Tables gif and gif present a list of interference filters for use at the WHT, either for narrow-band imaging, or as order-sorting filters for instruments such as TAURUS or UES.

The filters have been scanned using the Guildford Spectrometer at RGO. Results are not presented here, but ara available on the World-Wide Web servers at Cambridge and La Palma, where they will be updated when necessary. The measurements covered a region of about 5mm in diameter close to the center of the filters. The measurements were taken with the filters at room temperature. Note that temperature changes will affect the transmission; the central wavelength of an interference filter shifts to the red with increasing temperature, with a temperature coefficient of about 0.2 Å/degree C.

The transmission of an interference filter also depends on the angle of incidence of the light on it. This has the advantage that it is possible to fine-tune the central wavelength by tilting the filter; the central wavelength shifts to the blue with increasing tilt angle. For small tilt angles ( < 10) the effective wavelength is given by:

It should however be noted that tilting an interference filter also affects the bandpass and the peak transmission; the bandpass increases and the peak transmission decreases with increasing tilt angle.

Table: TAURUS-2 filters

Table: TAURUS-2 filters (continued)

Tue Aug 15 16:42:46 BST 1995