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    Re: Sextant calibration accessory
    From: Peter Monta
    Date: 2021 Feb 26, 21:07 -0800
    Hi Greg,

    I'm willing to beta test a set of these.  If a set of 16 are arranged in a 4x4 square then it becomes a single pocket instrument covering 10° to 80° at 5 ° increments .  I suppose each prizm would need to be calibrated just as a Bris.


    Sure, I'll certainly let you know once I have a decent prototype of either the calibration prisms or the standalone stacked-mirror sextant.  For the latter, what held me back for a while was the placement of shades.  If the two mirrors abut, it works fine for terrestrial objects, but there's really no place for the shades to go internal to the instrument without the risk of full-intensity solar glare, so solar observations are very awkward.  So I'm playing with this polygon arrangement "ABCDEF" where there are six stacked four-sided polygons.  A and D contain one set of angles, B and E another set, and C and F a third set.  This gives enough space for internal shades with a spacing of three polygons (about 9 mm, so a telescope aperture of 15 or 20 mm is enough), at the cost of needing a Keplerian telescope to fuse the noncontiguous entrance pupil.  I'll try to post a sketch at some point; maybe others can improve it further.

    The case you mention, though, of an array of fixed-angle sextants, is possible I think.  One could use either a pair of mirrors as with a conventional sextant, or transmissive prisms, pentaprisms for large angles and hexaprisms for small ones.  Interesting.  For naked-eye daylight use a 2 mm aperture is enough, so the whole thing would look like a fly's-eye with all the tiny prisms.  The downside is the small set of angles available.

    Cheers,
    Peter

       
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