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When TAURUS is used for imaging observations, the etalon wheel is empty and filters are mounted in either the focal plane filter wheel or the pupil plane filter wheel.
There are several factors to be considered when deciding which wheel to use for filters:
Before loading a filter in either of the filter wheels it must be mounted in a suitable holder. This should normally be done by the support astronomer and should not under any circumstances be attempted by inexperienced observers !
The access hatch for the focal plane filter wheel is on the side of the instrument, towards the top, and is labelled as such. In order to gain access to a particular filter wheel position, it is necessary to use the TFFILTER command to move the filter in the opposite position into the beam. For example, since there are 8 positions in the filter wheel, it is necessary to move the filter wheel to position 1 in order to change the filter in position 5. The access hatch can then be opened and the filter changed. There is no software lock on the access hatch, but the computer will detect and display its current status. An interlock prevents any of the TAURUS mechanisms, including the filter wheel, from being moved whilst the access hatch is open. Once all the required filters are loaded, it is necessary to use the TFNAME command to tell the computer where they are loaded, so that this information can be displayed on the mimic screen.
The access hatch for the pupil plane filter wheel is on top of the light table. It is not labelled. In order to open it, a special two--pronged tool is required, which is usually attached to the side of the instrument by a piece of string. The rest is as for the focal plane filter wheel, except that the TFFILTER and TFNAME commands are replaced by TPFILTER and TPNAME.