NavList:

Matt,

The difference in the horizon mirrors is two fold. The whole horizon doubles the usable field of view and more than doubles the overlapped image field. This gives the whole horizon the advantage of locating and setting the body on the horizon very quickly. The advantage of the split mirror is in the brighter overlapped image (a very narrow central vertical zone) so that dim stars in late twilight can be observed. Another more obscure advantage of the split horizon is in the taking of horizontal sextant angles where the images are separate and less confused. The sight tube has a larger field of view than any multi powered optic but I find that a 4 power optic is able to use the entire field of the horizon mirror whether split or whole so the tube has no advantage here. Where the sight tube shines is in the steady image it provides under adverse conditions. The tube also doesn't have any lenses to fog or smudge from ocean spray.

Greg Rudzinski

[NavList] Re: Sight Tube vs. 4x40mm Scope
From: ash13brook---com
Date: 23 Apr 2011 15:15

So, is the difference caused by the traditional mirror or the sight tube?
I ask because Mr. Burch at the Starpath School of Navigation does not seem to be a big fan of the whole horizon mirror and I am just curious as to others' opinions.
That said, I already have a sextant with a traditional mirror, and haven't had a chance to use it yet (Chicago winters are not too conducive to standing at the lakefront at twilight for any reason), so I have no opinion.
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