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The absolute calibration and characterization of the Multiband ImagingPhotometer for Spitzer (MIPS) 70 micron coarse- and fine-scale imaging modesare presented based on over 2.5 years of observations. Accurate photometry(especially for faint sources) requires two simple processing steps beyond thestandard data reduction to remove long-term detector transients. Point spreadfunction (PSF) fitting photometry is found to give more accurate flux densitiesthan aperture photometry. Based on the PSF fitting photometry, the calibrationfactor shows no strong trend with flux density, background, spectral type,exposure time, or time since anneals. The coarse-scale calibration sampleincludes observations of stars with flux densities from 22 mJy to 17 Jy, onbackgrounds from 4 to 26 MJy sr^-1, and with spectral types from B to M. Thecoarse-scale calibration is 702 +/- 35 MJy sr^-1 MIPS70^-1 (5% uncertainty) andis based on measurements of 66 stars. The instrumental units of the MIPS 70micron coarse- and fine-scale imaging modes are called MIPS70 and MIPS70F,respectively. The photometric repeatability is calculated to be 4.5% from twostars measured during every MIPS campaign and includes variations on all timescales probed. The preliminary fine-scale calibration factor is 2894 +/- 294MJy sr^-1 MIPS70F^-1 (10% uncertainty) based on 10 stars. The uncertainty inthe coarse- and fine-scale calibration factors are dominated by the 4.5%photometric repeatability and the small sample size, respectively. The 5-sigma,500 s sensitivity of the coarse-scale observations is 6-8 mJy. This work showsthat the MIPS 70 micron array produces accurate, well calibrated photometry andvalidates the MIPS 70 micron operating strategy, especially the use of frequentstimulator flashes to track the changing responsivities of the Ge:Ga detectors.

Absolute Calibration and Characterization of the Multiband Imaging Photometer for Spitzer. II. 70 micron Imaging