The NIRI filter wheels are 530mm in diameter and each contains 12 apertures for mounting near-IR filter. Filter wheel #1 is located immediately after the two fold mirrors and is in the uncollimated telescope beam. This filter wheel will hold broad band near-IR filters i.e. those not as sensitive to the collimated nature of the incident radiation. Filter wheel #2 is located after the collimator lens in the collimated beam and will hold narrow band near-IR filters e.g. interference filters for line and narrow band continuum work. Below is a photo of a filter wheel, in its protective and baffling housing, outside of NIRI. The design of the filter wheels (and the pupil mask/filter wheel) is modular in that the can be easily removed from NIRI.

The filter wheels slide into slots in the science path optical table. These slots can be readily seen in the photo below. Filter wheel #1 has its own slot while filter wheel #2 shares a wider slot with the pupil mask/filter wheel.

The photo below shows the two filter wheels and pupil mask/filter wheel mounted in the NIRI optical path, the collimator can be seen between the two filter wheels.

Below is a photo of a near-IR filter mounted in a filter holder and inserted into the NIRI filter wheel. The filters acquired for NIRI are from the Mauna Kea Filter Consortium set defined by the Gemini Observatory and University of Hawaii. The filters are 50mm in diameter and have optimised bandpass. See the NIRI imaging filters page for more information.

Filter wheel #1 sitting in its opened cassette:

Filter wheel #3 completely removed from its cassette. The five tilted red elements are the f/6 grisms(J,H,K,L,M), and the three clear ones are the f/32 grisms (J,H,K). The open position at the bottom is the pupil mask.