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    Re: Benefits of Stigmatizing
    From: Douglas Denny
    Date: 2010 Sep 26, 04:48 -0700

    Is there any refractive power in this lens?

    It might be a supplementary lens for someone with refractive eye error, and with a mark on it might be an astigmatic lens - in which case there should be a definite elongation of a star image through it. I still take my eye-glasses off for sextant use and have to adjust the telescope eyepiece for best image, which is not as good as if a proper correction is present: glasses make it difficult with the exit pupil of the telescope - reducing field of view.

    It might just have a mark however, to show which is the best position of the lens fitted to the telescope, as lenses up to post-WW2 possibly up to 1950s were hand-edged and were never a perfect circle so might fit better in a particular way in the fitting; or the brass fitting might be slightly oval and the same applies when fitted to the telescope.

    Douglas Denny.
    Chichester. England.
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