Display Status:

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 fillted metal box containing brass parallax sectors for the Sproul 24-inch refractor double-slide photographic camera. The original set contained 43 circular disks, each 40 mm in diameter with open notches ranging from 0.05% to 83%. A disk rotated rapidly above the center of the photographic plate in order to diminish the brightness of the program star at the center of the field.

Swarthmore College donated this set of objects to the Museum in 2017.

Collection Item Long Description:

Data Source

National Air and Space Museum

Restrictions & Rights

Do not reproduce without permission from the Smithsonian Institution, National Air and Space Museum


Credit Line

Donated by Swarthmore College


Mixed metals, etched painted wood.


3-D: 13.3 × 8.3 × 8.9cm, 1kg (5 1/4 × 3 1/4 × 3 1/2 in., 2.2lb.)



Inventory Number