  We present the reduction of the 24 micron data obtained during the first
cosmological survey performed by the Spitzer Space Telescope (First Look
Survey, FLS). The survey consists of a shallow observation of 2.5x2 sq deg
centered at 17h18m +59d30m (main survey) and a deeper observation of 1x0.5 sq
deg centered at 17h17m +59d45m(verification survey). Issues with the reduction
of the 24 micron MIPS data are discussed and solutions to attenuate
instrumental effects are proposed and applied to the data. Approximately 17000
sources are extracted with a SNR greater than five. The photometry of the point
sources is evaluated through PSF fitting using an empirical PSF derived from
the data. Aperture corrections and the absolute calibration have been checked
using stars in the field. Astrometric and photometric errors depend on the SNR
of the source varying between 0.35-1 arcsec and 5-15%, respectively, for
sources detected at 20-5 sigma. The flux of the 123 extended sources have been
estimated through aperture photometry. The extended sources cover less than
0.3% of the total area of the survey. Based on simulations, the main and
verification surveys are 50% complete at 0.3 and 0.15 mJy, respectively.
Counterparts have been searched for in optical and radio catalogs. More than
80% of the 24 micron sources have a reliable optical counterpart down to
R=25.5. 16% of the sources have a 20 cm counterpart down to 0.1 mJy and ~ 80%
of the radio-infrared associations have a reliable optical counterpart. A
residual map is obtained by subtracting point sources detected at the 3-sigma
level and interpolating the regions occupied by extended sources. Several
galactic clouds with low and intermediate velocities are identified by
comparison with neutral Hydrogen data from this field.

Astrophysics