256x256 Tilting Filters -- see graphs also!

The camera includes 2 1% bandpass filters whose center wavelength may be changed by tilting the filter. To move one of these filters into the beam, the plunger closest to the front of the camera should be positioned to mesh with a gear. The filter with the plunger pushed in almost to the dewar bottom is Brackett gamma while the other is a filter optimized for molecular hydrogen.

H2 Filter: 0.85" down from fully seated

Wavelength Tilt Line

2.121m m 13° H2 v =1 -> 0 S(1)

2.097m m 24° H2 continuum

Br gamma 0.05" down from fully seated

Wavelength Tilt Line

2.166m m 8° Br gamma

2.151m m 15° Br gamma continuum

How to Set the Tilting Filter

  1. Select filter and engage appropriate gears.
  2. Attach ohm meter.
  3. Check that turning between stops remains on linear part of potentiometer.
  4. IF turning between stops goes over the end of the potentiometer, re-enage gears so you remain in the linear range.
  5. Average readings at the two endpoints of rotation.
  6. Setting at this average puts filter normal to the beam.
  7. Tilt filter from normal position using graph of angle versus wavelength for the filter and the calibration in ohms/° .
  8. If possible, check setting on an astronomical source (eg. H2 cloud in Orion).