Thaw Refractor

Thaw Refractor

Main Optical Tube


Focal Length: 47 feet
Lens Diameter: 30 inches
Focal Ratio: f/18.8

Finder Scope


Focal Length: 96 inches
Lens Diameter: 8 inches
Focal Ratio: f/12
Eyepiece: 2 inch 50mm Erfle
Power: 48.8x

Guide Scope


Focal Length: 47 feet
Lens Diameter: 8 inches
Focal Ratio: f/70
Eyepiece: 1.25 inch 28mm RKE
Power: 511x
Under the largest dome is the Thaw Memorial Refractor.  William Thaw Junior, in memory of his father William Thaw Senior donated the funds for its construction.  The Thaw telescope was designed and built by the Brashear Optical company in 1912.  The lens of this telescope was designed for photographic use, it is corrected to bring blue light to a focus; this is where photographic films of this time were most sensitive.  The photographic program started in 1914 and to this day has collected some 110,000 exposures on glass plates.  It is one of the oldest and largest collections of photographic plates in the world.

In 1985 the original lens was replaced with one that is corrected to bring the red light to a focus.  The photo-multiplier tubes of the Multi-channel Astrometric Photometer (MAP) are more sensitive to red light.  Fortunately the Pittsburgh skies are still fairly dark in this region of the visual spectrum. 

The Telescope tube is 47 feet long and has a moving mass of about 8000 pounds.   Observers using the MAP work every clear night, including holidays.  The Thaw is currently doing stellar parallax work as well as looking for planets around other stars.     

Instrumentation:  Multi-channel Astrometric Photometer (MAP),  Finger Lakes Instruments IMG-4240 CCD Imaging Camera, 8 x 10 inch Photographic plate holder, 3.5 inch eyepiece for visual use. 



University of Pittsburgh
Department of Physics & Astronomy
Allegheny Observatory
159 Riverview Avenue
Pittsburgh, PA 15214

Last Modified 01/07/2023