Standard Photometer at the ESO 3.6-m

The Standard Photometer was mounted at the Cassegrain focus of the ESO 3.6-metre telescope at La Silla Observatory in 1981. This instrument was a single channel photometer fully operated from a control room.

The Standard Photometer had a diaphragm wheel, which was used to meet different seeing conditions. The wheel was slightly inclined to the plane of the image and the polished outer face of the wheel reflected the star field through the 3.6-metre TV viewing system in the Cassegrain adapter for data collection. This photometer used two diaphragms — one was used with the star being measured and the other measured the background sky. In total, 12 diaphragm sizes were used in the wheel, allowing four different combinations of star-sky positions. Eight filters were also available to the photometer and could be positioned automatically.

The photometer was used to observe stars no brighter than magnitude 10 and could be used in normal or fast (up to 10 kHz) photometric modes. The collected data were saved on a magnetic tape that could store up to 1.8 hours of measurements.

The Standard Photometer was decommissioned from the ESO 3.6-metre telescope in the 1990s.