Exchanging the filter

The filter holder was made for Filter B and is currently only suitable for filters of the same thickness. Filter A is just too thick. Filter C has not been tried (as of 16/9/2001). See also John Hart's email on interchangability problems.

Access to the filter is easiest via the square hatch on the flat side of the PN.S. Under no circumstances touch the filter with bare hands. Use the white gloves provided for this purpose in the PN.S cupboard.

Currently we only have one filter holder, which resides in the filter tilt mechanism. A picture of the filter unit is available as a doc file.

There are two wire rings; one retains the filter and the other retains the sleeve containing the filter. They both snap into grooves in their respective bores.

Both rings are secured by means of a tiny grub screw passing through the wall of the respective housing, and protruding into the narrow gap in ring. This spreads the ring diametrally to lock it in place. We included a drive key for the screws in the box containing the telescope adapter ring.

To remove the filter (from an email by John Hart 13/7/2001):

1. Remove the screws mounting the filter unit in the camera body, and withdraw the filter unit unit from the camera body.
2. Place the unit "face down" on a clean flat surface.
3. Retract the grub screw that locks the outer wire ring, and remove that ring by prising one end out of the groove. Be careful!
4. Remove the spring ring.
5. Slide the inner cell (filter and sleeve assembly) out of the outer housing. This gives access to the grub screw that locks the inner wire ring.
6. Retract the grub screw that locks the inner wire ring, and remove that ring.
7. Slide the filter and associated pack rings out of the sleeve. You will need surgical style gloves to avoid getting finger prints on the filter.

To install the filter, reverse the foregoing procedure. Note that the shiny side of the filter goes face down so that when the filter unit is (inverted and) installed the shiny side is facing the collimator.

!! UPDATE THE PNS HEADER CREATER GUI !!

The procedure is tedious, but it can easily be done during the day.

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