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Wolfgang,
Thanks. This is all that I wanted to know about Bris.

Alex.

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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