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    Re: Getting to know a sextant.
    From: Tony Oz
    Date: 2017 Mar 6, 08:34 -0800

    Hello!

    I spent the whole Sunday on a beach practicing sights. Got several lunar attempts (Sun-Moon and Venus-Moon) but because of the shore layout the proper procedure was not possible (the Moon was over the land/forest near me).

    An observation:

    • when the sextant arm is set to high degrees (~70° and above) the index mirror appears in the horizon mirror as a narrow strip. At 120° the index mirror is no more than ~6~8mm wide as seen through the ghost ring and does not occupy all the reflective half of the horizon mirror. The center line of that strip is located slightly above the middle of the horizon mirror - i.e. parallel to its' horizontal diameter but ~5~7mm above it.

    Does that mean that ideally the axis of the scope (or the center of the ghost ring) should be aligned so that the narrow strip of the index mirror - when set to 120° - is seen exactly in the center of the viewing field? I can draw a sketch of what's going on if my description is not clear.

    When angles are relatively small - the index mirror is wider (in vertical direction) than the field of view and I can use monocular simply put to the ghost ring (by hand). But at high angles I have to tilt the scope slightly up to get the correct image. Now even a scope-less sight is difficult to take if big angles are involved.

    Please comment.

    Warm regards,

    Tony

       
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