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    Re: Some Link A12 Sextant Questions
    From: Tracy Shrier
    Date: 2018 Jan 21, 14:36 -0800

    David,

    Airborne a few nights ago I tried some indirect viewing on stars. With preset altitudes to make sure I had the right star, I could find the stars reflections off the index glass to the sides of the bubble chamber image fairly easily. I know I attenuate light through the windshields, so getting the bubble image dim enough to see the overlay of the star, then maintaining bubble/star alingment with turbulence and plane oscillations with the dim image is much harder than with direct viewing. Sirius was no problem, but even magnitude 1's Procyon and Rigel were essentially not doable in the plane. 

    Regarding battery life, it's possible that your rheostat is not switching completely off. I had to pull mine apart and rebuild. I've attached some pictures. Look down the battery tube to see if the rheostat pole comes completely off the windings in the off position. Also check to see if there is an insulator (paper or plastic, the blue disc pictured) between the battery contact and the rotary mechanism underneath. At any rate, I pull my batteries out of the holders when not using.

    I found some xylene for my bubble chambers and I do have to add some to bring the bubble smaller every several months as well. The lead washers that seal the glass have probably oxidized or otherwise given way. I've painted shellac on those lead seals on one of my chambers to try to seal, and put a dollop on top of the filler screw after closing, it's maybe helped a bit. 

    I had the '5° error' a few times last year as I got started. I have convinced myself of operator error as one sight would be off and the other one or two would work out, I never a a situation of all sights being 5 off. I either mis-read the vernier before pulling the disk for the next shot, or have spun the disk off the series of sight marks and then rotated it back to the wrong alignment before reading the vernier. If all of your sights are off, then it looks like calibration is needed. I've calibrated mine as recommended by Mr. R. Swartz by zeroing on a water horizon and then sighting Polaris for index error.

    Tracy



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