  ULTRACAM is a portable, high-speed imaging photometer designed to study faint
astronomical objects at high temporal resolutions. ULTRACAM employs two
dichroic beamsplitters and three frame-transfer CCD cameras to provide
three-colour optical imaging at frame rates of up to 500 Hz. The instrument has
been mounted on both the 4.2-m William Herschel Telescope on La Palma and the
8.2-m Very Large Telescope in Chile, and has been used to study white dwarfs,
brown dwarfs, pulsars, black-hole/neutron-star X-ray binaries, gamma-ray
bursts, cataclysmic variables, eclipsing binary stars, extrasolar planets,
flare stars, ultra-compact binaries, active galactic nuclei, asteroseismology
and occultations by Solar System objects (Titan, Pluto and Kuiper Belt
objects). In this paper we describe the scientific motivation behind ULTRACAM,
present an outline of its design and report on its measured performance.
