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User-supplied Filters

GMOS users may supply their own filters for queue observations. The policy for doing so and the specifcations for the filters needed are given below.


  1. The users should indicate clearly in their PhaseI proposal that they intend to supply their own filter(s).
  2. The users should indicate clearly in their PhaseI proposal whether they already have the filter(s) needed, or whether they will be purchased at some later time.
  3. The users should ship the filters to Gemini ahead of their observations. The filters need to arrive at Gemini a minimum of two weeks before they are first needed for use in the instrument.
  4. The users should supply with the filters measured transmission curves as a function of wavelength.
  5. The users are encouraged to leave the filters in the instrument for the full semester, in order to increase the probability that observations will be obtained for their programs.
  6. Since filters for GMOS are of a size that is unlikely to be useful in other instruments, Gemini also asks that the users supplying their own filters consider letting the filters stay in GMOS for use by the community.


  1. Outer diameter 160mm (+0.0mm -0.2mm).
  2. Clear diameter 150mm.
  3. Gemini filters are made to the following specification: Transmitted wavefront errors which contribute to wavefront deformations greater than the `power' term (which would generate a defocus in the camera) to be less than lambda/4 (p-v) at 633nm over any 100mm diameter patch within the clear diameter. It is recommended that user supplied filters are made to the same specifications. Relaxing this specification impacts the delivered image quality.
  4. The filters should be designed to use in a parallel beam of light.
  5. Maximum overall thickness of the filter allowed by GMOS is 10mm.
  6. Optical-quality glass with no pinholes.

Contact information

After approval of their program for queue observations with Gemini, the users should contact their assigned contact scientist regarding how to proceed with supplying their own filters. The contact scientist will put the users in contact with the appropriate Gemini Staff members.

Last update February 23, 2002; Inger Jørgensen