MIPS delivered diffraction-limited imaging capability at all three wavelengths due to the matching of the pixel scales to the width of the Spitzer PSF. In the wide field of view mode at 70 microns the pixels are slightly too large to achieve lambda/2D sampling of the PSF, so observers who were particularly interested in getting the highest possible spatial resolution at 70 microns should have utilized the narrow field of view (''super resolution'') mode. In addition, image quality at the corners of the 24 micron field of view is slightly degraded. Off-center variation in PSF only applies to the 24 micron band models, and not to the longer wavelength bands. Variations of the PSF over the array in the 70 and 160 micron model images appear to be negligible
Figure 2.2 is an example of the 24 micron PSF at the array center (T = 5000 K). The PSF is strongly centrally peaked with a well defined first Airy ring. For bright astronomical sources with a very high signal-to-noise ratio, the full extent of the PSF might be visible in the MIPS images. The telescope secondary mirror support ''spiders'' result in the radially extending artifacts in the PSF. We note that these images are theoretical, Tiny Tim PSFs and not actual data. The model PSFs are very close to the measured in-orbit PSFs. The point spread function (PSF) in the MIPS bands is not highly sensitive to small changes or differences in telescope and instrument optical parameters. The MIPS PSF images are dominated by the telescope optics, not the internal instrument optics.
Figure 2.2: (Top) A 24 micron PSF with the display parameters stretched to show the central peak and first ring only. (Bottom). The same 24 micron PSF with the display parameters stretched to show the full PSF in the same 5 x 5 arcminute field of view.
