  The CFRS 1452+52 field has been deeply imaged with the Infrared Space
Observatory (ISO) using ISOCAM through the LW3 filter (12-18um). Careful data
analysis and comparison to deep optical and radio data have allowed us to
generate a catalog of 78 15um sources with both radio and optical
identifications. They are redder and lie at higher redshift than I-band
selected galaxies, with most of them being star-forming galaxies. We have
considered the galaxies detected at radio and 15$\mu$m wavelengths which
potentially include all strong and heavily extincted starbursts, up to z=1.
Spectral energy distributions (SED) for each of the sources have been derived
using deep radio, mid-IR, near-IR, optical and UV photometry. The sources were
then spectrally classified by comparing to SEDs of well known nearby galaxies.
By deriving their FIR luminosities by interpolation, we can estimate their Star
Formation Rate (SFR) in a way which does not depend sensitively on the
extinction. 75% (-40%, +10%) of the star formation at $z \le 1$ is related to
IR emission and the global extinction is in the range Av=0.5 -- 0.85. While
heavily extincted starbursts, with SFR in excess of 100 Mo/yr constitute less
than a percent of all galaxies, they contribute about 18% of the SFR density
out to z=1. Their morphologies range from S0 to Sab, and more than a third are
interacting systems. The SFR derived by FIR fluxes is likely to be ~2.9 times
higher than those previously estimated from UV fluxes. The derived stellar mass
formed since the redshift of 1 could be too high when compared to the present
day stellar mass density. This might be due to an IMF in distant star-forming
galaxies different from the solar neighborhood one, or to an underestimate of
the local stellar mass density.
