The pupil viewer optics are used in conjunction with the f/32 camera to produce an image of the pupil (the Gemini secondary, M2) on the near-IR detector. This is very useful for alignment purposes. The pupil viewer optics consist of three spherical lenses of diameter 60mm which are made of ZnSe (2) and BaF2. The photo below shows one of the lenses in it position in NIRI but out of the telescope beam. The f/32 camera barrel has been removed and would normally be positioned between the mount labelled 'optical path' and the beam splitter mirrors to the right (not in the photo).

Below is a photo of the second pupil viewer lens, located below the optical table, in the withdrawn position.

Below is an (unflattened) L-band image of the pupil taken in June 2006. The pupil fills approximately 90% of the array with a spatial resolution of about 3-4mm on the surface of the secondary (M2) mirror.