The JWST Near Infrared Imager and Slitless Spectrograph (NIRISS) instrumentation includes internal optical components, filters, grisms, and an aperture mask to support its four observing modes.
- Transfer optics:
- a pick-off mirror (POM), which also includes the focus mechanism,
- a three-mirror assembly (TMA) to collimate the incoming beam, and
- a camera TMA to focus light on the detector.
- Pupil and filter wheels as a dual-wheel assembly:
- filters—12 bandpass filters (seven wideband and five medium-band) distributed equally between the pupil and filter wheel;
- in the filter wheel that operate between 0.8 and 2.2 μm with R ≈ 150. These grisms are identical but oriented to disperse in orthogonal directions on the detector;
- GR700XD—a grism in the pupil wheel that operates between 0.6 and 2.8 μm with R ≈ 700, which is optimized for applications that require high spectro-photometric precision; and
- a non-redundant aperture mask (NRM) in the pupil wheel that enables high spatial resolution imaging with medium contrast.
- Detector: a single Hawaii 2RG sensor chip array with 2048 × 2048 pixels. Each pixel is 18 × 18 μm and provides a plate scale of 0.0654 × 0.0658 "/pixel.