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The Multiband Imaging Photometer for Spitzer (MIPS) provides long-wavelength capability for the mission in imaging bands at 24, 70, and 160 m and measurements of spectral energy distributions between 52 and 100 m at a spectral resolution of about 7%. By using true detector arrays in each band, it provides both critical sampling of the Spitzer point-spread function and relatively large imaging fields of view, allowing for substantial advances in sensitivity, angular resolution, and efficiency of areal coverage compared with previous space far-infrared capabilities. The 24 m array has excellent photometric properties, and measurements with rms relative errors of about 1% can be obtained. The two longer-wavelength arrays use detectors with poor photometric stability, but a system of onboard stimulators used for relative calibration, combined with a unique data pipeline, produce good photometry with rms relative errors of less than 10%.

We have used the Submillimeter High Angular Resolution Camera (SHARC) bolometer camera at the Caltech Submillimeter Observatory to map the distribution of the broadband 350 km continuum emission toward the Orion A molecular cloud. A comparison of the 350 km Ñux densities in OMC-1 with previous 1100 km measurements indicates a strong spatial variation of the grain emissivity exponent, b. The lowest value of the exponent (b^1.75) is found toward the Orion Bar photon-dominated region (PDR), while the highest value (b^2.5) is found toward the Orion Ridge north of IRc2. This variation is consistent with the destruction of grain mantles by the UV photons from the Trapezium cluster. The observed spatial variation of b in OMC-1 suggests that the long-wavelength grain emissivity may also vary signiÐcantly in GMC cores on small linear scales pc), a †ecting column density and mass ([0.5 H 2 estimates. The 350 km continuum emission in the Orion Bar region correlates well with the CO (6È5) peak brightness temperature and is shifted by D10A from the molecular component traced by the 13CO (6È5) emission. This indicates that the 350 km dust emission in this region originates predominantly in the outer high-temperature PDR layers. Several Ðlamentary structures previously detected in molecular tracers are also seen in our map at Ñux levels comparable to those seen in the Bar. Over 30 compact dust sources are detected in the OMC-2 and OMC-3 clouds, including a dozen sources not previously known. The average 350/1300 km Ñux ratio based on our data and previous observations of this region (63^19) indicates low dust temperatures (17^4 K, assuming b \ 2) for most of the sources. The brightest 350 km source in OMC-3 has a low 350/1300 km ratio (D23), indicating a very low dust temperature (D10 K), or a signiÐcant opacity at 350 km (D2.5). This source appears to be a deeply embedded and cold young protostar. A comparison of the mass estimate for the OMC-2/3 Ðlament based on the 350 km continuum emission with previous C18O mass estimates indicates a relatively high grain emissivity, Q(350) \ 4 ] 10~4, in this region.