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    Re: Mylar Film as Artificial Horizon Windows
    From: Robin Stuart
    Date: 2011 Mar 15, 17:39 -0700

    The particular mylar used was actually the Baader Planetarium TurboFilm referred to in my post. It is specifically intended as an optical window. I obtained it from Woodland Hill’s Camera & Telescopes at the link http://telescopes.net/doc/2500/mftr/baader/item/TURBO Other types of mylar film may work too. In general thinner is better.

    The fogging that I mentioned in the post also happens with the plastic and glass windows supplied with the Davis artificial horizon but at a slower rate. I don’t it think would be advisable to apply anything (onion juice, saliva etc.) to the windows as this might affect its optical properties and hence the sextant altitude readings. It is probably better just to let the water equalize in temperature with the air before putting on the windows. (Of course this only works if the temperature is above freezing which it often wasn't around the time the observations were made). Alternatively one might substitute sump oil or mercury for the reflecting surface in which case fogging should not be a problem.

    Robin Stuart
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