Near-Infrared Imaging Spectrograph (NIIS)

The optical design of NIIS consists of a traditional collimator/camera design to enable the image scale to be reduced for a more optimal sampling of the image point spread function on the detector. The optical design was made By Charles Harmer (NOAO) and is similar to that of FLAMINGOS. This cross section illustrates the optical components and their mounts. From left to right are seen the three lens "stacks" within their mounting tubes. At left is the fused silica vacuum window followed by the corrector stack. The corrector is located just forward of the telescope focal plane to improve the off-axis images of the telescope. The second assembly is the collimator stack used to collimate the beam of the telescope and image the pupil of the telescope. The design is basically a Cooke Triplet and a field lens near the telescope focus to image the pupil between the collimator and camera assemblies. The right-most assembly is the camera stack. The camera reimages the collimated beam with a scale reduction of about a factor of three to better match the seeing at APO to the pixel size of the detector.