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    Re: Having trouble
    From: Randall Morrow
    Date: 2012 Jan 9, 08:24 -0800

       Are you using a "first-surface mirror"?     The quality of the mirror is likely not as important as this question.   Particularly at lower altitudes, the two reflections from the front and back of normal second surface mirror, will cause the image to degrade from a pin-point to a blur.       Even with the many fine scratches caused by setting a level on the mirror in close to a thousand observations, I still get pin-point reflections.   As for the lower end, here is where the first surface mirror comes in to it's own, with no ghost images.   You may have to stand 15 to 20 feet back from the mirror to get them but I shot a moon lower limb recently at about 11 degrees.    The difficulty is houses and trees blocking low shots, not the a.h..

       The horizon filters on the Davis were not intended to look directly at a reflection of the sun.   I have tried supplementing mine with dark film given to me by G.R, and also with home made filters popped out of 3-D movie glasses.   Hold the lenses up and turn them relative to each other until the polarizing effect gives you the shading you need.   Cut these to shape and tape them on the outer horizon filter frame.   Just leave them taped in place and fold that shade down when you shoot the sun.  

       Of course the a.h can't be used for bodies over about 60 degrees but you have to shoot what you've got.    At sea you would seldom get an ideal sky what with clouds, fog and indistinct horizons.      The story of the development of the 'Sumner line' is a good example of this.     There will likely never be a chance for me to get on a boat to do any real navigating, but there is still the enjoyment of watching the march of the constellations across the sky.    Get the list of the navigational stars visible in your hemisphere and good hunting!    

    Randall F Morrow PT
    Kern County - Bakersfield


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