It was reported that in some cases when moving the filter wheel in ALFOSC the system notes that the filter did not arrive and the FITS header shows the filter status as `MOVING'. It is thought that the wheel actually does move and arrives in the right place but that the system status gets confused.

We are checking at what encoder position the filter wheel was at those times where the filter header says `MOVING' during observations which constantly switched between 2 filters. If the wheel moved properly the encoder position should be different from that during the preceding and subsequent observations but the same as the ones one step further removed. This will at least show that there is no problem with the data itself, though the issue of the wrong status will still have to be solved.

Thomas Augusteijn 2009-05-14