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Etalons can be loaded into positions 1, 2, 4 or 5 of the etalon wheel. Positions 3 and 6 are intended as clear positions, and have no cabling for etalons. Note that each position in the etalon wheel which has cabling for an etalon must always contain either a real or dummy etalon, properly cabled up. Otherwise loose cables can be snagged when the wheel is moved.
In order to access a particular position in the etalon wheel, it is necessary to move it into the light-table, by moving the opposite position into the beam.
Etalons are loaded into the etalon wheel through the access hatch for the pupil-plane filter wheel, which is located in the top of the TAURUS--2 light-table. In order to cable up the etalon it will also be necessary to open the access hatch for the etalon wheel, which is located in the bottom of the TAURUS--2 light-table. Both hatches are opened using a special two-pronged tool, which is usually attached to the side of the instrument with a piece of string.
In order to access the etalon wheel from the top of the light-table, it is necessary to move the pupil-plane filter wheel so that the large hole in this wheel is located in the light table position. Do this by putting position 5 of the pupil plane filter wheel into the beam.
When changing an etalon it is convenient to disengage the detent pins for the etalon and pupil plane filter wheels, so that they are not clamped. This will make accessing the etalon in order to connect wiring more straightforward. To do this, the parameters used when requesting the wheels to move should be negative. For example, in order to change the etalon in position 1 of the etalon wheel, issue the following commands from the instrument control computer:
The procedure to change the etalon is as follows: