The 12K×8K CCD mosaic camera for the Palomar Transient Factory

The Palomar Transient Factory is an automated wide-field survey facility dedicated to identifying a wide range of transient phenomena. Typically, a new 7.5 square degree field will be acquired every 90 seconds with 66% observing efficiency, in g' band when the sky is dark, or in R band when the moon is up. An imaging camera with a 12Kx8K mosaic of MIT/LL CCDs, acquired from CFHT, is being repackaged to fit in the prime focus mounting hub of the Palomar 48-inch Oschin Schmidt Telescope. We discuss how we have addressed the broad range of issues presented by this application: faster CCD readout to improve observing efficiency, a new cooling system to fit within the constrained space, a low impact shutter to maintain reliability at the fast observing cadence, a new filter exchange mechanism, and the field flattener needed to correct for focal plane curvature. The most critical issue was the tight focal plane alignment and co-planarity requirements created by the fast beam and coarse plate scale. We built an optical profilometer system to measure CCDs heights and tilts with 1 μm RMS accuracy.