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    Sextant Filters / Nearsighted CelNav?
    From: Greg R_
    Date: 2006 Apr 23, 14:53 -0700
    Hi All:
    I learned CelNav (at least the theory part) years ago, and I'm getting back into it here recently - even went out and bought a sextant over the weekend (Davis Mk 25, which I've pretty much figured out how to use) so I can practice "the real thing" instead of just reading about it and trying to follow along vicariously.  :-)
    Two questions come to mind that I haven't been able to find in any of my CelNav books:
    1) What (if any) is the specific usage for the different-colored filters (i.e. blue, amber-orange, grey, etc.)? I know that for a really bright sun you'll normally want to have all of them down (4 in my case), but is there ever any case where you'd want to use them either singly or in combinations? I would guess that the amber-orange one could be used on the horizon to sharpen it up on a hazy day, and the grey one obviously knocks down the brightness a bit, but where would you use the blue one(s) (mine has two of them) or maybe other combinations?
    2) How do you near-sighted navigators cope with the problem of finding stars through the sextant? I can see now how that might be a challenge (I'm about 20/100) - I was able to pull down Jupiter without any problem, but Polaris was a lot harder to do (granted, it was on-and-off cloudy that night, maybe I'll have better luck on a clear night).
    What I've been doing so far is locating the star with my glasses on, lining myself up directly facing it and then aiming the sextant in the general area. That worked fine for a bright body like Jupiter, but I have my doubts about using it to pick a navigational star out from the others. Though I was able to pick Antares out from the others in Scorpio, so maybe it gets easier with practice(?) - the 1st magnitude stars do tend to stand out from the others.
    Thanks in advance for any input, it's nice to finally be able to practice what I'd read about all those years ago.  :-)
    Los Angeles, CA
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