Removing filters from the wheel

We have latex gloves that can be used to handle filters. They are packaged in a box with a fine drying powder, so it is best to wash this off before use. Cotton gloves would be a good future investment.

To remove and replace filters in the wheels, the following procedure has worked well:

1. The filter wheel is placed flat on a table with the filter to be replaced positioned so that it overhangs the edge of the table. Lens paper is put down underneath the wheel to protect the filters. The side of the filter wheel through which the filters are accessed should be placed facing upwards.
2. A special white plastic filter wheel tool (labeled as such) is available and stored with the filters. It is used to screw in and unscrew plastic rings which are screwed down on top of each filter, holding the filter securely against the filter wheel at the bottom of the hole.
3. To remove one of the rings, slide this tool into the hole and down on top of the ring, fitting it into the notches on the ring. Unscrew the ring in the normal counter-clockwise direction. Once the ring is unscrewed, remove it carefully so that it doesn't come into contact with a filter.
4. To insert a ring, place it on the top of the hole and get the ring threaded initially by hand. Then hold the filter wheel tool by the metal knob and screw the ring down onto the filter. Once the ring contacts the filter, it will tighten and the metal knob will turn separately from the plastic tool. This mechanism is designed to limit the torque applied to the ring and protect the filter.
5. To remove a filter, push it up from beneath with one hand, touching only the outer parts of the filter if possible. Once free of the wheel, the filter can be grabbed around the edges using the other hand.
6. Each slot in the filter wheel has a number between 1 and 9. The number for the slot is printed on the side of the wheel directly opposite from the slot. Note the positions. The filter positions are given to the observatory software using a look-up table which will have to be updated if there are changes.