Re: Sextant Error and Whole Horizon Mirrors
Subject: Re: Sextant Error and Whole Horizon Mirrors
From: Jared Sherman (jared.sherman@XXX.XXX)
Date: Tue Jul 09 2002 - 21:55:29 EDT
Chuck-
I looked at my sextant after reading your message (can only take sights on Canadian Forest Fire Smoke tonight) and realize that although both the index and horizon mirrors do have a "tilt" adjustment, the two have their adjustment screws set at different points (i.e. one at 3 o'clock, the other near 8 o'clock) so that no matter how the two are adjusted, there is really no provision for making them completely co-planar in left-right alignment. (I *think* my geometry and physics are good enough to be sure of that.<G>)
That would mean that unless you can find a particular model of sextant where the tilt alignment screws are both at 3 or 9 o'clock, you would have to depend on the alignment of the frame as a whole--or use a split mirror, or place a vertical mark on your whole mirror, such that you are only working on one vertical line (i.e. where a split would be) rather than across the whole width of the mirror.
I would think that a craftsman with very good hands could either adjust one mirror frame, or (safer) shim the mirror out as needed to try making it more fully parallel to the other mirror.
I wonder if this error is simply inherent to whole mirrors and ignored in them, or if any maker has taken pains to allow it to be corrected out?
