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    Re: Bris does not work
    From: Alexandre Eremenko
    Date: 2012 Jul 29, 17:38 -0400

    Thanks. This is all that I wanted to know about Bris.
    On Sun, 29 Jul 2012, Wolfgang Hasper wrote:
    > Hi all,
    > Sven Yrvind notes in his blog/website
    > http://www.yrvind.com/present_project/
    > "Several years ago i invented the Bris minisextant as a
    > navigational toy and back up to the GPS. There is a
    > video on youtube ? search Yrvind.
    > Yesterday I got a thelephone call asking if the
    > surfaces where coated .
    > There is no coating. Not on the production type nor on
    > any experimental prototypes. It would not work on this
    > kind of sextant.
    > I use ordinary flat panel glass. When I was a small
    > child living on the windward side of a small island I
    > noticed, and was intriged by the fact that the windows
    > in our house was transparent in the daytime and
    > mirrors at night when it was dark outside. I remember
    > that I asked my grandmouther about about that very
    > interesting and curious  fact but she could not give
    > me an satisfactory ansver. I never forget it and
    > thougt that one day I may have use of it. Now I now
    > that windows are beamsplitters. 90% transparent and
    > 10 % reflective.
    > In the 3-glass sextant one can see eight images of the
    > sun. (in the 4-glass sextant many more). One of the
    > glasses is a filter to reduce the strenght of the sun.
    > It is very balanced not to bright not to dark. To
    > enable the observer to see the 3 bright suns created
    > by dubble reflections and the 5 dim suns created by
    > quadrupple reflections at the same time. People have
    > fat on their fingers. The fat creates fingerprints. If
    > fat or dirt gets on the sextants optical surfaces it
    > may reduce the transparency and only the bright suns
    > may be seen.
    > If this happens the sextant should be cleaned. I use
    > ordinary disch washing detergent. After rinsing I dry
    > the surfaces with compressed air ? oil-free compressed
    > air. Like what people use for diving or cleaning
    > negatives. If you do not have acces to clean
    > compressed air try to centrifuge away the water use
    > the cord attached to the sextant, attatch a little
    > weight to it to gove more inertia, swing swiftly, do
    > not hit anything.
    > The outer surfaces are easy. For the inner ones one can
    > use a dentalfloss-houlder and cotton thread ? do not
    > use dental floss as it is waxed.
    > The sextant is glued with a specially formulated
    > NM-epoxy that chemically reacts with the glass. You
    > can clean with anything that does not harm epoxy and
    > glass."
    > Am Freitag, 27. Juli 2012 21:37 schrieb Ken Gebhart:
    >> Greg and others,
    >> We sold the Bris for many years, and there was no
    >> silvering on the glasses. The glasses were smoked
    >> glass, although the very first ones had clear glass
    >> for use with stars.  I just spoke to Sven Yrvind on
    >> the phone, and he still makes 1 or 2 per year and
    >> sells them personally. He did say that at one time
    >> after he went out of formal production, he
    >> experimented with a beam splitter coating.  So maybe
    >> you have seen one of those.
    >> Ken Gebhart
    >> On Jul 27, 2012, at 12:20 PM, Greg Rudzinski wrote:
    >>> Here is a diagram of first and second reflections.
    >>> If this is not correct then someone please chime
    >>> in.
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