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From: Alexandre E Eremenko (no email)
Date: Mon Apr 24 2006 - 09:51:01 EDT
Dear Greg,
> 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
Some sextants have all filters of the same color.
My one has 2 yellow of different intensity
and a light grey on each mirror
+ very dark red on the index.
Even for the brightest Sun, I never use ALL filters together.
But various combinations can be used in various conditions
for various tasks. Sextant is designed not only for taking Sun's
altitudes, but for measuring all sorts of angles. For example
the angles between the objects on the shore. In which case, I would use
to light yellow filetrs to surpress haze. Sometimes I have to
use one of the lighter filters on the Moon or even a bright star
at night. You want to make the two objects to look approx equally bright
while really they can be of very different brightness.
> 2) How do you near-sighted navigators cope with
> the problem of finding stars through the sextant?
I am not near-sighted but still this causes some problems sometimes.
a) Take your sextant up side down, point (and focus for your eye) on the
star, and then search for the horizon. Once you found it, revert the
sextant to the normal position.
b) Pre-compute (or take the approximate value from the
star finder) and pre-set the altitude.
c) Detach the scope. Using your normal eyeglasses, you can catch
the star and the horizon to your field of view, and even bring them
together. Now attach the scope, and refine the altitude.
Alex.
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