  The Palomar Transient Factory (PTF) is a project aimed to discover transients
in the Universe, including Type Ia supernovae, core-collapse supernovae, and
other exotic and rare transient events. PTF utilizes the Palomar 48-inch
Telescope (P48) for discovering the transients, and follow-up mainly by the
Palomar 60-inch Telescope (P60, for photometric light and color curves), as
well as other telescopes. The discovery rate of PTF is about 7000 candidate
transients per year, but currently only about 10% of the candidates are being
followed-up and classified. To overcome this shortcoming, a dedicated
spectrograph, called the SED Machine, is being designed and built at the
California Institute of Technology for the P60 Telescope, aiming to maximize
the classification efficiency of transients discovered by PTF. The SED Machine
is a low resolution (R ~ 100) IFU spectrograph. It consists of a rainbow camera
for spectrophotometric calibration, and a lenslet array plus 3-prism optics
system for integrated field spectra. An overview of the science and design of
the SED Machine is presented here.
