Aperture Wheels

There are two aperture wheels in Clio. The first is at the image plane (field stop wheel) which is the Cassegrain focus. The second is at the image of the telescope secondary (pupil wheel). Each of these are six position wheels accepting 1 inch diameter masks. The wheels contain the following masks. The listing is clockwise from the home position.

Field Stop Wheel

Last updated October 2010.

  • Small pinhole (home) (50 microns?)
  • Open
  • Wide slit
  • Medium slit
  • Narrow slit
  • Large rectangle (size of f/20 field)


    • The image below shows the position of each of the slits in the Field Stop wheel. The narrow, medium, and wide slits are centers on rows 90, 260, and 532 respectively.

    Note that all slits appeared to be the same width of approximately 0.5” The slits are oriented parallel to the coldplate.


    Pupil Wheel

    Last updated 22 Aug. 2012 for Clio2:

  • f/20 stop = 4.33mm (home) (was f/20 - 4.95 mm - for Clio1)
  • M band phase plate
  • L’ band phase plate
  • f/35 stop = 3.32mm (was f/35 - 3.8 mm for Clio1)
  • 3 hole Nonredundant mask
  • 6 hole Nonredundant mask
  • Pupil stops

    • Clockwise from Phil's hand: 3-hole non-redundant aperture mask; 6-hole non-redundant aperture mask; Wide-camera (f/20) cold stop (home); M-band apodized-phase plate; L'-band apodized-phase plate; Narrow-camera (f/35) cold stop.