  The Zwicky Transient Facility (ZTF) Observing System (OS) is the data
collector for the ZTF project to study astrophysical phenomena in the time
domain. ZTF OS is based upon the 48-inch aperture Schmidt-type design Samuel
Oschin Telescope at the Palomar Observatory in Southern California. It
incorporates new telescope aspheric corrector optics, dome and telescope
drives, a large-format exposure shutter, a flat-field illumination system, a
robotic bandpass filter exchanger, and the key element: a new 47-square-degree,
600 megapixel cryogenic CCD mosaic science camera, along with supporting
equipment. The OS collects and delivers digitized survey data to the ZTF Data
System (DS). Here, we describe the ZTF OS design, optical implementation,
delivered image quality, detector performance, and robotic survey efficiency.
