KPNO SINGLE CHANNEL POLARIMETER
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  Instrument Overview                                                         
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    The Single-channel Polarimeter was put into service for the Kitt Peak 36- 
    and 50-inch telescopes in August 1969.  It is similar to one built at the 
    Crimean Astrophysical Observatory (Shakhovskoy and Dymov 1962).  The main 
    element of the device is a rapidly rotating polarizer mounted in a        
    circular disk containing 100 radial slots spaced uniformly around the     
    perimeter.  The disk serves to encode the angular position of the         
    polarizer.                                                                
                                                                              
    A star-chopping technique is used to compensate for sky brightness by     
    means of a pair of closely matched diaphragms in the focal plane.  The    
    remainder of the polarimeter includes a moveable filter slide immediately 
    following the polarizer, and then a Lyot depolarizer.  The final optical  
    element is a CuSO4-5H2O crystal in a moveable slide which is used to      
    eliminate red leaks from the shorter-wavelength filters.                  
                                                                              
    The observing procedure is to place a star in one diaphragm with an area  
    of adjacent sky in the other.  Small systematic differences between the   
    two beams are eliminated by periodically switching the star from one      
    diaphragm to the other during an observation.  The observer is aided by an
    oscilloscope display of the accumulated intensity as a function of        
    polarizer position angle.                                                 
                                                                              
    For further information about the instrument, including a schematic       
    diagram, see Dyck and Sandford (1971).                                    
                                                                              
    Dyck, H.M and M.T. Sandford II, Multicolor polarimetry of some Mira       
    variables, Astronomical Journal 76, 43-49, 1971.                          
                                                                              
    Shakhovskoy, N.M. and N.A. Dymov, Publ. Crimean Astrophys. Obs. 27, 291,  
    1962.

References
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Dyck, H.M and M.T. Sandford II,         
        Multicolor polarimetry of some Mira variables, Astronomical Journal   
        76, 43-49, 1971.

Shakhovskoy, N.M. and N.A. Dymov, Publ. 
        Crimean Astrophys. Obs. 27, 291, 1962.