GP70 History

The mirror is the mate to the Samuel Oschins Telescope mirror at Palomar. They were two 72 inch blanks cast in the 1940’s by Corning. Palomar took the better of the two.

In July 1988 Debra Medlock finds the second of the two blanks for sale in Sky and Telescope. Soon Group 70 is formed and 25,000 dollars is raised to purchase the glass.

In 1989 the glass arrived in SanFrancisco.

In 1989 through 1998 the mirror was edged from 72 inches to about 71 1/2 inches, the back is ground flat, the curve on the glass is reduced from F2 to F2.89, and fine grinding and polishing are completed.

In June 1993 the first optical test was completed. It was a perfect sphere.

The next ten years were spent figuring the surface.

Finally in 2003 the mirror reached 1/3 wave.

August 2003 it was determined that the metal strap holding the mirror upright for the test was deforming the surface and no further meaningful work could be done until the mirror cell was complete.

December 2003 Group 70 lost its funding. The mirror had to be stored until more money could be raised and construction of the telescope could begin.

2005 A roughly 85,000 dollar grant was donated to Group 70. However, it was a challenge grant and could not be used until two matching grants could be attained.

2003-2014 The corporation storing Group 70’s mirror was up for sale. The mirror and its accompanying equipment was moved to one of the Barosso Family Farms warehouses in the Central Valley. Dan Zuras announced that he was stepping down from the Group 70 presidency and Dave Barosso took over as president.

2014-present. The telescope design was updated, the donated money accrued to the required amount stipulated by the challenge grant, with the help of Michael Barosso and legal council the insurance issues were resolved, a workshop was least in MacArther Ca., the mirror transported to the new shop, and work started on the telescope tube assembly.

The the best of our knowledge Group 70 is the largest privately funded telescope and mirror that has been ground, polished, and figured by Amateur astronomers.

For more reading and access to our archived records about the project press here Please be advised that the archives are continually being adding to as we work through 32 years of records….