A returning issue when mounting instruments at the Cassegrain focus at the bottom of the adapter has been that of the screw holes used to mount the different instruments losing their thread so they can no longer be used. In the current situation typically only half of the existing holes available for a given instrument are used. However, these holes (on the adapter plate and the instrument mounting plate) are not specifically prepared for the type of screws and precise alignment required for each instrument. It was decided to do this in a slightly different way, preparing the new holes with the instrument mounted such that there should not be an issue of alignment between the holes on the mounting plate and the adapter. This has already successfully be done for NOTCam. For the FASU filter unit, to which either ALFOSC or MOSCA is attached, this is slightly more complicated as the holes can only be accessed from inside the unit, and we probably need to make a special tool for this.

Thomas Augusteijn 2013-05-10