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    Re: Dual sight holes in antique octants?
    From: Bill Morris
    Date: 2012 Feb 5, 15:12 -0800

    Noell

    I think the two holes have the same function as the rising piece on a sextant with a telescope : to give a larger view of the horizon. With a telescope, more light from the horizon enters the 'scope when it is moved further from the frame of the sextant and even a relatively small increase in light intensity results in a disproportionately larger increase in contrast, thus improving the view of the horizon.

    One might think that with a pinhole, one has only to move the eye a little to the side to see more horizon, but this results in a very much smaller view of the observed body, compared to moving the pinhole. This is easier to experience than to explain, so I suggest you remove the scope from a sextant, substitute a bit of card with a 1 to 2 mm hole in it and play with it to see what I mean.

    Bill Morris
    Pukenui
    New Zealand
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