This object is not on display at the National Air and Space Museum. It is either on loan or in storage.
Collection Item Summary:
This is a "Double-Slide" photographic plate holder for the 24-inch Sproul refractor at Swarthmore College, Swarthmore, PA. It contains a Schott OG 515 yellow filter plate (2 mm thickness) and rectangular insert for 5x7 inch photoographic plates. Similar to designs developed by G. W. Ritchey for the Yerkes Observatory and built by Charles Riddell, this plate holder contains a 40 mm rotating sector system to reduce the brightness of program stars to ranges compatible with field stars, a standard astrometric technique for stellar parallax and proper motion studies. It was purchased and used by Peter van de Kamp and others at Sproul Observatory in the late 1960s in their continuing search for unseen planetary companions to other stars. The plate holder upgrade was part of a general overhaul of the telescope system, which started in May 1966 and lasted through the rest of the year.
Swarthmore College donated this set of objects to the Museum in 2017.