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Geoffrey,

I have two box sextants:

 An Elliott Bros with shades that only cover the sky portion and not the horizon. But, it has a movable eyepiece that can be completely open, show a small pinhole, or show a pinhole with a shade that would cover both the sky and horizon and would allow a sun shot with an AH.

A  J. Hicks that was advertised as a military version.  The normal two pivoting shades also just cover the sky mirror. It has the same type of sliding eyepiece but with a wide open position to allow a (missing) telescope, a relatively open half circle on the bottom of the slide, and a pinhole. No eyepiece shade at all. Not for AH and the sun.

Many box sextant descriptions refer to their portability for use in engineering and surveying. I suspect that complete shading might not be needed in that area.

I'm probably going to add some kind of temporary external shade to the J. Hicks that won't do any permanent damage.

Noell