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Are you saying the flare only appears when the sun is reflected in
the clear part of the horizon glass?  It will be reflected off both
the front and back surfaces there.  Normally that's not a problem,
since these surfaces are parallel, and the fraction-of-an-inch
difference in the light paths is negligible over 93 million miles!
But if those surfaces are no longer parallel, or if the index
mirror isn't perfectly flat (more likely IMHO), you could see a
double image.

What do you see without the telescope?  Does it depend on the
altitude you're measuring?
        -- Bill

-----Original Message-----
From: Navigation Mailing List
[mailto:NAVIGATION-L@LISTSERV.WEBKAHUNA.COM] On Behalf Of Jim Thompson
Sent: Wednesday, July 06, 2005 5:35 AM
To: NAVIGATION-L@LISTSERV.WEBKAHUNA.COM
Subject: Flare artifact


My sextant has developed an annoying flare artifact.  It appeared the
other
day when I was doing sun sextant shots on a very bright summer forenoon.
I
was using a split mirror and the 6x telescope (Astra IIIb)  The flare
appeared around the right half of the sun when the sun's image was in
the
left side of the field of view, but vanished leaving a clean image of
the
sun if I moved the sextant so the image was over the black half of the
field
of view on the right.

I cleaned all the shades, the horizon glass, and both external surfaces
of
the telescope's lenses (ie front and back), but no imrovement.

Any suggestions?  Sounds to me like I might have a problem inside the
telescope.

Jim Thompson
jim3 at jimthompson dot net
www.jimthompson.net
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