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    Mylar Film as Artificial Horizon Windows
    From: Robin Stuart
    Date: 2011 Mar 13, 11:57 -0700

    Gary Lapook describes the construction of an artificial horizon with large glass windows http://www.fer3.com/arc/m2.aspx?i=115348&y=201101
    An alternative material to use would be mylar film which is nowadays used in its aluminized form as a safe solar filter for white light observations of the Sun through a telescope. David Burch in his book “How to use a Plastic Sextant” talks about using it for sextant sun shades.

    Mylar’s use as an optical window dates back to an article in Sky and Telescope, July 1978, p.67 by Peter Sahula who describes using it to cover the slit in his observatory dome allowing him to observe from a heated room during the New York winter. There is a later paper by Laird A. Thompson, Astronomical Society of the Pacific Publications 102 (1990) 1086 available at
    which studies it further.

    High quality unaluminized mylar is marketed by Baader Planetarium under the name TurboFilm. It is the same film used in the solar filters which they also manufacture. The thing to bear in mind about mylar windows and filters is that they are not pretty to look at. The mylar should be left a bit loose and not pulled tight so that it flops around just a bit. Initially it seems hard to imagine that that this would work but the mylar is effectively optically invisible.

    I have constructed mylar windows for a Davis artificial horizon with a frame cut from poster foamboard and attached it with double-sided tape. With foamboard the frame needs to be relatively broad and it might be better cutting a narrower one from a sheet of rigid plastic. Initial sights show that the windows work very well indeed. If the air temperature is lower than that of the water in the artificial horizon then some fogging may occur.

    Robin Stuart

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