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    Re: Tinkering with Davis sextant scope
    From: Rolf Vainio
    Date: 2011 Apr 11, 03:03 -0700

    Thank you for the positive comments.

    Yes the small 12mm aperture of the Opticron monocular has backsides,
    Low light performance is not the best and that last shot at nautical twilight into a washed out horizon might even succeed with the original Davis when the 4x12 Opticron has to give up. The latter is notably darker when light fades out. Physiology also plays in, the older one gets the lesser the difference ,at my age =67 the pupil will not expand beyond 4.5mm with my eyes adapted for near darkness (= 9 candela). Therefore in that situation I can only accommodate about half of the light coming out from the Davis 7.1mm exit pupil but all of that presented by the Opticrons 3 mm exit pupil, so for me the difference between the two is hardly notable but a person aged 25 with a 6mm pupil would have a different experience
    (the pupil sizes where extracted from this study : http://www.iovs.org/content/35/3/1132.full.pdf ).

    The other still untested consideration is that due to the small exit pupil, aligning the Opticron might prove problematic when in a small boat and being tossed around by a gale.

    Having said the above I can live without that last shoot in near darkness and enjoy the increased field of view and handling improvement the whole rest of the day.

    Rolf Vainio
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