IRAC: Instrument Description: Optics

The Spitzer focal plane with the IRAC apertures indicated.

IRAC Cryogenic Assembly Model, with the top cover removed to show the inner components.

Light from the telescope is reflected into the IRAC structure by the pickoff mirrors for the two fields of view (FOVs). Each pair of channels has a doublet lens which re-images the Spitzer focal plane onto the detectors. A beamsplitter reflects the short wavelength light to the InSb detectors (Channels 1 and 2) and transmits the longer wavelength light to the Si:As detectors (Channels 3 and 4). Channels 1 and 3 view the same telescope field (within a few pixels), and Channels 2 and 4 view a different field simultaneously (see figure above). However, the orientations of the sky on the InSb arrays are flipped with respect to the Si:As arrays by the beamsplitter. The edges of the two IRAC fields of view are separated by approximately 1.5, with no overlap on the sky. The IRAC pixel scale is nearly the same in all channels (~1.2 arcsec per pixel), providing a 5.2x5.2 arcmin FOV.

See also the PSF page.

For more information, see the IRAC chapter of the SOM

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