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    Re: Moon's 4SD
    From: Frank Reed CT
    Date: 2006 Nov 10, 18:28 EST
    Bill, you wrote:
    "I have to admit, I hate eye glasses for cel nav with any amount of light
    pollution on land, as well as on the water in general unless absolutely
    necessary. "
     
    Hey, I feel your pain. <g>
     
    Seriously, I know it's a nuisance, but there is really no other choice if you have significant astigmatism. A sextant telescope can accommodate a wide range of changes in focus so people who are near-sighted can get excellent results by re-focusing the scope, but astigmatism implies a different focus for different orientations of your eye. There is no realistic way to cancel that out except with eyeglasses (until you're ready for eye surgery).
     
    No "realistic" way?? So how about something unrealistic: ask your optometrist what they would charge to make you a prescription telescope for your sextant... :-) Or, you could learn to look through your sextant sideways, or maybe at a 30 degree angle. :-) If you know the orientation of the cylindrical deformation of your eye, you could arrange to keep that axis parallel (or perpendicular) to the frame. Then focus there. After all, it only matters that the image should be in focus in the "up and down" direction through the sextant. If it's blurred "left and right" (perpendicular to the frame), that doesn't hurt and sometimes it even helps --so much so that some sextants come with "astigmatizer" attachments designed to turn star images into horizontal lines.
     
    -FER
    42.0N 87.7W, or 41.4N 72.1W.
    www.HistoricalAtlas.com/lunars

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