× 0. Palomar Observatory
M. Visitor Center (Museum)
H. Hale Dome

The 48-inch (1.2-meter) Samuel Oschin Telescope

Palomar Observatory’s 48-inch Samuel Oschin Telescope is one of the most productive survey telescopes ever built with a dozen completed surveys since the 1950s. The wide-field imaging capabilities of this telescope (it has a usable field hundreds of times larger than that of the 200-inch Hale Telescope) makes it ideal for conducting systematic surveys of the sky. In recent years, the Samuel Oschin Telescope has been used to scan large regions of the sky to search for transient events—objects that change apparent brightness and/or position—such as fast-moving Solar System objects, variable/pulsating stars, flares, novae, supernovae, gamma-ray bursts and other stellar explosions. It currently operates robotically, scanning the skies nightly and returning a wealth of astronomical data.

The telescope was dedicated as the Samuel Oschin Telescope in 1987, in recognition of the prominent adventurer, entrepreneur, and philantropist’s passion for astronomy and generous support to the observatory.


The Samuel Oschin Telescope (originally the Palomar 48-inch telescope) is a special-purpose device, designed and built to add broad reconnaissance capabilities to the Palomar Observatory portfolio. Compared with the Hale Telescope which excels at detailed study of individual objects and systems, the Oschin Telescope’s strength is surveying large segments of the sky efficiently. The telescope was dedicated as the Samuel Oschin Telescope in 1987.

As originally conceived Palomar Observatory was to be focused solely on the Hale Telescope; the idea of broad reconnaissance in general and the Oschin in particular was an afterthought suggested by astronomers Walter Baade and Fritz Zwicky. The Oschin is a so-called Schmidt telescope or camera that delivers a usable field of view hundreds of times larger than that of the Hale. The Schmidt concept was first demonstrated on sky at Palomar in 1936 with an 18-inch Schmidt telescope, currently on exhibit in the Visitor Center. Performance of the 18-inch was so promising that Caltech committed to building the Oschin in the late 1930s, and the telescope saw first light in September 1948.

The Oschin is famous in astronomy for enabling many sky surveys—notable among them are the Palomar Sky Surveys in two different instances in the 1950s and the 1990s. Insights from these surveys have touched all areas of astronomy: from solar system dynamics to study of galaxy clusters—the largest bound structures in the universe. Discoveries made with the Oschin famously led to the reclassification of Pluto as a dwarf planet in 2006.

Throughout most of its history the Oschin used photographic techniques—glass plates with photographic emulsions that would be exposed and developed to produce images. However over the last two decades the Oschin has been fitted with increasingly capable electronic cameras. Modern electronic detectors are much more light-sensitive than photographic emulsions. In present day the Oschin hosts a 600-megapixel camera, and is the discovery engine for the Zwicky Transient Facility. The Oschin operates purely robotically; there are typically no astronomers or staff present in the dome during observations, but instead the data are linked around the world in near-real time.

Upcoming guided tour.