  The IMACS Cluster Building Survey uses the wide field spectroscopic
capabilities of the IMACS spectrograph on the 6.5m Baade Telescope to survey
the large-scale environment surrounding rich intermediate-redshift clusters of
galaxies. The goal is to understand the processes which may be transforming
star-forming field galaxies into quiescent cluster members as groups and
individual galaxies fall into the cluster from the surrounding supercluster.
This first paper describes the survey: the data taking and reduction methods.
We provide new calibrations of star formation rates derived from optical and
infrared spectroscopy and photometry. We demonstrate that there is a tight
relation between the observed star formation rate per unit B luminosity, and
the ratio of the extinctions of the stellar continuum and the optical emission
lines. With this, we can obtain accurate extinction-corrected colors of
galaxies. Using these colors as well as other spectral measures, we determine
new criteria for the existence of ongoing and recent starbursts in galaxies.
