Binocular Question

From: Mir16609@aol.com
Date: Wed Apr 11 2001 - 14:21:00 PDT

  • Next message: Matson, Robert: "RE: Binocular Question"

    For satellite observation (and general astronomy
    observation) I've been using the "Relative Brightness
    Index" as the measure for rating a binocular's ability
    to gather light.  This index is defined as the exit
    pupil diameter divided by the magnification and
    multiplied by the objective diameter.
    
    For 7x50s the index is 51
    For 10x50s the index is 25
    For 12x50s the index is 17
    For 7x35s the index is 25
    For 20x60s the index is 9
    
    Lately I've read about the "Twilight Factor" which is suppose to be a measure of the binocular's ability to
    contrast objects in low light conditions.  This is
    defined as:
    the square root of (magnification * objective diameter).
    
    For 7x50s the factor is 18.7
    For 10x50s the factor is 22.4
    For 12x50s the factor is 24.5
    For 7x35s the factor is 15.7
    For 20x60s the factor is 34.6
    
    Which index is a better indicator for a pair of
    binocular's ability to detect a dim LEO object?
    
    With the Relative Brightness Index it would appear to
    be 7x50s.  With the Twilight Factor it would appear to
    be 20x60s.
    
    Cheers,
    Don Gardner  39.1799 N, 76.8406 W, 100m ASL
    http://hometown.aol.com/mir16609/
    
    -----------------------------------------------------------------
    Unsubscribe from SeeSat-L by sending a message with 'unsubscribe'
    in the SUBJECT to SeeSat-L-request@lists.satellite.eu.org
    http://www2.satellite.eu.org/seesat/seesatindex.html
    



    This archive was generated by hypermail 2b29 : Wed Apr 11 2001 - 14:21:58 PDT