Imaging Modes Spectrum Image
Available for NIRCAM, NIRISS and MIRI
NIRCam has two modules, each with a field of view of 2.2x2.2 arcminutes. Within each module, the light is split with a dichroic and sent to a short-wavelength (0.6-2.3 μm) and a long-wavelength (2.4-5 μm), channel which observe simultaneously. The short-wavelength channel has a scale of 0.032" per pixel, which Nyquist samples the PSF at 2 microns. The long-wavelength channel has a pixel scale of 0.065". Each channel has a selection of wide-, medium- and narrow-band filters.
NIRISS is capable of imaging from 0.8 to 5 μm with a field of view of 2.2x2.2 arcminutes. It uses a spare filter set from NIRcam and has a pixel scale of 0.065" per pixel, which matches the sampling of the NIRCam long-wavelength channel. In general, NIRCam is the camera of choice for near-infrared imaging with JWST, since it has twice the field of view of NIRISS and obtains "blue" and "red" images simultaneously. Used in parallel with NIRCam, NIRISS can potentially increase the resultant sky coverage at these wavelengths.
MIRI provides broad-band (R~5) imaging from 5 to 27 μm over a field of view of 74x113 arcseconds, with a pixel scale of 0.11".
Available for NIRISS
Available for NIRCAM and MIRI
For observations from 5-28 μm, MIRI has four individual coronagraphs, one of which is based on the classic design of Lyot and three of which are based on four-quadrant phase masks (4QPMs). The classical Lyot coronagraph places an occulting spot in the focal plane to block the light from a bright point source from entering the instrument, resulting in an inner working angle of 2.1". It is intended for observations at ~23 μm.
The 4QPMs in MIRI use an optical element that retards the phase by π in two diagonally opposite quadrants. If a monochromatic source is placed exactly at the center of the resulting four-quadrant phase mask, the rejection is formally complete. Working with spectral bandpasses of ~10%, the 4QPMs have inner working angles of 0.3-0.5", with contrasts in the range 10-3 – 10-4 for a source separation of 1".