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This is a blink stereo comparator microscope manufactured about 1960 by the C. Ridell Company of Williams Bay, Wisconsin for the U. S. Naval Observatory. It is typical of a class of discovery devices used in photographic astronomy from the late 19th through the 20th centuries to detect variable stars and asteroids, and high-proper motion stars. Two photographs of the same part of the sky were placed side by side in parallel microscopes that through a set of mirrors combined the two images, allowing the observer to switch rapidly between the two aligned scenes. Anything in the field of view that changes becomes visible through a shifting or pulsating image. In this design, the usual viewing eyepiece has been replaced with a system that projects images of the plates onto a circular screen. This reduced the fatigue of this tedious operation, which sometimes could take decades. It was transferred to NASM by the U S Naval Observatory in 1996.

 Display Status

This object is not on display at the National Air and Space Museum. It is either on loan or in storage.
Object Details
Country of Origin United States of America Type EQUIPMENT-Scientific Devices Manufacturer C. Ridell Company
 Dimensions 3-D: 114.3 × 61 × 94cm (3 ft. 9 in. × 2 ft. × 3 ft. 1 in.)
3-D (Table): 114.3 × 71.1 × 71.1cm, 29.9kg (3 ft. 9 in. × 2 ft. 4 in. × 2 ft. 4 in., 66lb.)
3-D (Storage Dimensions Table & Microscope Parts): 152.4 × 121.9 × 91.4cm, 65.8kg (5 × 4 × 3 ft., 145lb.)
3-D (Bulb, Microscope Parts): 14 × 3.8cm (5 1/2 × 1 1/2 in.)
3-D (Black Lenses (2), Microscope Parts): 7.6 × 2.5cm (3 × 1 in.)
3-D (Brass Lens, Microscope Parts): 5.7 × 2.5cm (2 1/4 in. × 1 in.)
3-D (Black Fragment, Microscope Parts): 15.2 × 3.2cm (6 in. × 1 1/4 in.)
3-D (Plug, Microscope Parts): 20.3 × 17.8 × 2.5cm (8 × 7 × 1 in.)
3-D (Paper Filter, Miscroscope Parts): 11.4cm (4 1/2 in.)
3-D (Wires, Microscope Parts): 10.2 × 10.2cm (4 × 4 in.)
3-D (Switch Box, Microscope Parts): 21.6 × 12.7 × 8.3cm (8 1/2 × 5 × 3 1/4 in.)
3-D (Variable Speed Control, Microscope Parts): 17.8 × 17.8 × 10.2cm (7 × 7 × 4 in.)
 Materials HAZMAT: possible cadmium; Cast iron, anodized aluminum, optics, electrical components, light bulbs.
 Inventory Number A19960303000 Credit Line Transferred from the U.S. Naval Observatory, Washington, DC Data Source National Air and Space Museum Restrictions & Rights Usage conditions apply
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