urn:nasa:pds:context:instrument:multi-host.dbp 1.0 1.10.0.0 Product_Context 2020-06-12 1.0 Creation McCord, T.B., A Double Beam Astronomical Photometer, Applied Optics, vol. 7, pp. 475-478, 1968. Dual Beam Photometer Photometer Instrument Overview =================== The dual beam photometer is designed to provide object and sky photoelectric photometry through a series of 24 filters. The light passes through a field lens and then through a 24-position filter wheel the positions of which are selectable by means of a stepper motor. The next element in the optical path is a chopping mirror which alternates at a rate of 24 Hz between the object and a nearby patch of sky. The resulting beam then enters the detector. A choice among three different available detectors was made on the basis of the required sensitivity and wavelength range for the given object. The three available detectors include a high quantum efficiency GaInAs photomultiplier, an S-20 photomultiplier, and an S-1 photomultiplier.