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    Re: Hello and a question about polarizer sun filters
    From: Bill Lionheart
    Date: 2016 Dec 6, 09:03 +0000

    Polarizing filters are for removing reflected light from the sea
    surface. The filters on a sextant for attenuating the sun light are
    very dark, of course and should be comfortable for viewing the sun.
    That said I am interested to hear what you say about training in
    astronomy. Considering the very elaborate safety training I got for
    using lasers, basically a day of being told not to look in to  lasers
    (visible or IR), been shown pictures of the damage to eyes from
    looking in to lasers, and then doing calculations of power per area on
    the retina for different  types of lasers (and a test at the end),  I
    was trying to recall what training I got on my RYA Yachmaster Ocean
    Theory course.  We didn't see much sun as it was in the winter so we
    were just told to start with the darkest filters. That was it. There
    seems so much potential for damage to the eyes here!
    
    Bill
    
    On 5 December 2016 at 23:13, Wayne Hilliard  wrote:
    > I want to say hello and introduce myself. I have been interested in
    > celestial navigation for many years. In the past I have played with a
    > plastic Davis sextant and a artificial horizon. I finally decided to get a
    > metal sextant and study this in greater detail. To that end I have joined
    > this list and am scheduled to take the introductory class that Frank Reed
    > holds at Mystic. I look forward to becoming more knowledgeable in this
    > field.
    >
    > Anyways let me get to my questions. I purchased a Navy Mark 2 sextant on
    > Ebay for not much money at all and was very pleased to find that it is 100%
    > there. Including a spare index mirror and horizon mirror. The only thing
    > missing is the lid of the box the sextant is stored in.  I took it this
    > weekend and did some sun shots with it. This sextant has adjustable
    > polarization filters. Being a amateur astronomer I am very aware of eye
    > safety and viewing the sun. Common wisdom is that this type of filter is not
    > eye safe. However I am aware that filters on sextants don't seem to follow
    > with what is taught in the astronomy field. Now with the filters adjusted to
    > maximum darkness the sun still seemed to be to bright for me to be
    > comfortable doing it.
    >
    > I guess I have 2 questions. Is this type of filter safe to use and assuming
    > that these are the original filters could they have degraded with age. I
    > have contacted the Robert White Company in Boston and have gotten pricing on
    > overhauling this sextant and replacing the filters with new polarizers.  But
    > would like to have input from the folks on here about this subject.
    >
    > Thanks in advance!!!!
    >
    > View and reply to this message
    
    
    
    --
    Professor of Applied Mathematics
    http://www.maths.manchester.ac.uk/bl
    

       
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