Large spectrograph for use at Cassegrain Focus

Bill Rehrig and Larry Steimle of Boller and Chivens

Larry Steimle and Chet Wheeler of Boller and Chivens

Larry Steimle of Boller and Chivens

Cassegrain Focus Spectrograph. 61 Inch U.S. Naval Observatory Telescope, 1968

The observer was Ed Fengler; Boller and Chivens master instrument assembler.
At a meeting hosted by Bill Baustian of Kitt Peak National Observatory, a discussion was entered into for the need of small, portable lightweight duel-beam optical telescope.
Bill Baustian sketched a blackboard rendering of which Don Winans of Boller and Chivens took a Polaroid photo. From that blackboard sketch, Don Winans of Boller and Chivens designed the instrument.
Boller and Chivens manufactured 8 to 10 of these site-survey telescopes.
The telescope would be designed specifically for determining the seeing conditions in the selection of possible observatory sites. It needed to be lightweight to be transported possibility by pack animals and easy to repeat set-ups at that site for different seasonal surveys.
A 40” separation was selected as the nominal diameter in determining the minimum observing window area for acceptable air current disturbances.
The instrument would gather two images of a selected star. The two incoming star image beam paths at 40” apart with each beam passing through an optical flat turning mirror.
A pair of 6” objective lens combined each of the two star images at a common focal point.
A single eyepiece would have the two images in its field of view.
These two images would then be focused on a clear reticule plate with circular scribed diameters of
2-sec, 4-sec and 6-sec of arc separations.
When the instrument was setup at a selected site, the amount of moving deviations of the double star images on the reticule would be recorded
Returning at later time, again observations would determine how stable the observing was at that site and would be recorded and compared from different seasons.

The first Boller and Chivens project involving telescopes was the Right Ascension and Declination slow motion drives for the 120 Inch Telescope at Lick Observatory at Mount Hamilton, California.Phantom Telescope Dome Computer transmits telescope’s Right Ascension and Declination position to automatically align the dome’s azimuth rotational positions and the dome slits vertical opening size.