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    Sextant scopes and an old-bold empiricist
    From: Bill B
    Date: 2006 Apr 13, 16:02 -0500

    I've been comparing a few "straight" lower-magnification (approx. 3X to 4X)
    and higher-magnification (6X to 8X) prism sextant scopes .
    I have a few questions:
    1. How many lens elements should I expect to find in 3X to 4X power
    "straight" scopes?
    2. How many lens elements should I expect to find in 6X-8X prism scopes.
    3. How many lens elements should I expect to find in a 6X inverting scope?
    (I know Alex has the answer to this, as he has disassembled his SNO-T
    inverting scope).
    4. Does the f-ratio (focal length over objective lens diameter) hold up for
    prism optics?
    Now the sticky wicket--determining magnification. Problem at hand, no lab,
    no optical bench, no degree in optical engineering.  I need to take sextant
    scopes with no specs (except diameter of objective lens, and determine their
    respective magnifications.
    All I can figure is to focus all the scopes with a given eye, solidly tripod
    mount them, put shades (filters) in front of the objective lens to protect
    the (glue?) mounting of lenses/prisms from the heat (noting an astronomy
    caution that telescopes can take the heat, but binoculars cannot), and point
    at a known object (sun?).
    Then introduce a target (piece of white board) behind the exit pupil and
    move them to bring the sun's projected image into sharp focus (like viewing
    the sun through a telescope and projecting it onto a piece of paper/board).
    Measure and compare the diameter of the projected circles to the sun's SD.
    (Caveat here being that image size will change as the scopes focus--barrel
    extension--is changed. Hence common focus. Much easier if the magnification
    of one of the scopes is known as a reference.)
    Any thoughts would be appreciated.

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