One of the plastic rings that holds filters in place on the wheel is slightly oval in shape. This means it is difficult to screw into place. In January 2005, this ring is in slot 3 of filter wheel 2 and holds the narrowband [SII] 6717 Angstrom filter in place. It would be best to avoid removing this filter if possible.
Don Walter notes that for the narrowband filters, central wavelength is measured at 10C (50F). The central wavelength is expected to shift 0.1-0.2 Å per degree C in the same direction as the temperature change.
The software should disable the wheels when not rotating them.
The numbering is 1-9 since the wheels are stamped with numbers and I want to be consistent with this.
The home flag is at about filter position 8.25.
Warning:There is some confusion as to which wheel is named the "Upper" and "Lower" filter wheel. I will follow EOS notation that the "Upper" filter wheel is actually the upper when taken out of the telescope. In the telescope it is the wheel closer the floor. It is FW1.
The "Lower" filter wheel is FW2 and on the telescope is farther from the floor. Because of this confusion, I will try not to use the terms Upper and Lower, but instead say FW1 and FW2.
See sections 5.2.1 and 5.2.2 for the relevant operating software.