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    Re: Scopes and old-bold...
    From: Alexandre Eremenko
    Date: 2006 Apr 16, 17:13 -0400

    Just tried the "fence method" proposed by George,
    for the scopes mentioned in my message
    "Testing scopes", Apr 16, 15:48:08 EDT,
    I obtained:
    Scope A: Magnification 6x, field of view 5d
    Scope B: Magnification 8x, field of view 7d
    Used several fences nearby, 2 binoculars,
    of known magnification and two
    sextant telescopes of known magnification and
    field of view (one with wires that simplify the business:-)
    On the number of lenses (question asked by Bill).
    My inverting scope has 3 lenses.
    One is the objective lens, and two constitute a
    Ramsden eyepiece (achromatic).
    I suppose, together with George, that prismatic
    scopes have the same number of lenses, 3.
    Two will not be enough because of chromatic aberration.
    By the way, Chauvenet in volume 2, describes 4 methods
    of finding the unknown magnification of a telescope.
    One of them is essentially the "Sun method" proposed by
    Bill, another is equivalent to the "Fence method" proposed by
    And here is another one.
    Focus the scope carefully and direct it to the bright blue sky.
    Put a screen of white paper behind the eyepiece, and you will see
    a white disc. Measure the diameter of this disc.
    The ratio of the objective lens diameter to the diameter
    of the disc is the magnification.

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