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    Re: Bris does not work
    From: Wolfgang Hasper
    Date: 2012 Jul 29, 21:05 +0200

    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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