WHT flat-field lamps

Dome flats are typically obtained by pointing the telescope at the inside of the dome at some intermediate zenith angle e.g. ZD = 45 deg (to avoid the structured background near the top of the dome), and switching on one or more of the five lamps (9, 25, 150, 500, 500 W) mounted on the top-end ring (push-button controls on the old 'engineering' desk in the control room). There's no flat-field screen at the WHT.

The relative intensities delivered by the different top-end lamps are given below, for 3 different settings of the potentiometer knob (on the control desk) = minimum / black mark / maximum. The numbers are peak counts per sec delivered in an ACAM spectrum, probably around 8000 A, and the ratios between the intensities will be different at other wavelengths.

 
LAMP           COUNTS/SEC

'9 W'          40 / 60 / 110

'25 W'         [Not yet tested]

'150 W'        4000 / 6000 / 8000

'500 W'        9000 / 12000 / 19000

Note that the potentiometer knob provides a range of only ~ 2 in intensity.

A tripod-mounted lamp is also available, usually somewhere on the Nasmyth walkway. It's bright - don't look directly at it when it is powered on.

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Last updated: 3 February 2013