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Jacobus Kapteyn Telescope

PP: People´s Photometer

First light: August 1996.

Description: During the 80s the most often scheduled of the f/15 instruments for the Kapteyn Telescope was the People´s Photometer. It was designed in the 70s by R. Bingham at the RGO and five were built for various observatories throughout the world. These instruments are conventional two-channel photoelectric photometers, most frequently used in a star-sky mode where the separation of the two apertures is 172 arc sec. Each channel has an independent filter slide to take six filters; typically Kron Cousins ubvri or Strömgren uvby and Hß. When the transparency is variable it is possible to use only one aperture and put a neutral beam-splitter immediately behind it which sends the light into the two different photomultipliers. By selecting different filters for the two channels one may measure colours in non-photometric conditions even when it is impossible to measure magnitudes; the best example is the Hß index. It is possible to replace the neutral beam-splitter with a Foster prism which forms a polarizing beam-splitter, and at the same time insert a rotating waveplate in the beam above the aperture. This combination modulates the light from a polarized source by an amount proportional to its polarization. A half-wave plate produces a modulation at four times the frequency of the plate rotation which is solely dependent on the linear polarization of the source. A quarter-wave plate is also sensitive to the linear polarization but the modulation has only half the amplitude; however there is an additional modulation at twice the plate frequency proportional to the circular polarization of the source.

Clearly the People´s Photometer allows the astronomer to choose between a variety of configurations to study the particular problem he has in mind. 

Publications (scientific papers, technical publications, etc.).

Peoples Photometer Quick Guide

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Contact:  (Public Relations Officer)
Last modified: 22 August 2016