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    Re: Horizon filters not dark enough for a.h.
    From: Gary LaPook
    Date: 2011 Oct 14, 10:35 -0700

    The only problem with this is that you may be introducing additonal refraction error. But, it instead of placing your variable polarizing filter in front of the horizon mirror you put it at the sighting tube or telescope any refraction will affect both images equally so won't affect the measurement.

    gl
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