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Re: Question about Davis Mk 25 sextant beam converger
From: Greg R_
Date: 2006 May 7, 22:08 -0700
From: Greg R_
Date: 2006 May 7, 22:08 -0700
Hi All:
Thanks for all of the good input on the Mk 25 beam converger. I took it
Thanks for all of the good input on the Mk 25 beam converger. I took it
to the beach this past weekend and got a good
alignment on both the sun
and the horizon, and it seems to be working OK -
I'm getting intercepts using
a known (GPS)
position of anywhere from 1/2 mile to ~3.5 miles (using Navigator
Light to compute
the Hc and Int), and I'll just ignore the close-in parallax
"errors".
Fred: I hear you on being careful not to "over-adjust" it for errors, but I did need
Fred: I hear you on being careful not to "over-adjust" it for errors, but I did need
to get a good initial calibration (something that
I couldn't seem to do in the backyard),
and from what I understand plastic sextants are a
lot more susceptible to IE than
the metal ones. In fact, the Davis instruction
manual seems to recommend adjusting
it whenever it's used ("Adjusting your sextant is
easy and should be done each time
it is used."). Maybe that's why they put knurled
adjustment screws on it instead of
regular screws?
BTW, don't know if this has been done before, but I came up with a slightly
off-the-wall method of "faking" a horizon since the sun's dec is now too high
BTW, don't know if this has been done before, but I came up with a slightly
off-the-wall method of "faking" a horizon since the sun's dec is now too high
to get a LAN shot with an artificial
horizon at my latitude (34°14.9' N):
I took a length of surveyor's string and attached one end to the side of the
house at my eye height, with the other end attached to a tripod also set at
my eye height (and checked for horizontal with a carpenter's line level).
From across the backyard (~20') I'm able to get "reasonable" LOPs - the
intercepts on those are running anywhere from 3.7 to 8 miles (though I do
get the occasional one that's way out of the ballpark, so this method isn't
perfect. In fact, I can induce a several-minute error by slouching slightly
vs. standing up straight).
Even if it's not accurate enough for real navigation, it did serve its purpose
I took a length of surveyor's string and attached one end to the side of the
house at my eye height, with the other end attached to a tripod also set at
my eye height (and checked for horizontal with a carpenter's line level).
From across the backyard (~20') I'm able to get "reasonable" LOPs - the
intercepts on those are running anywhere from 3.7 to 8 miles (though I do
get the occasional one that's way out of the ballpark, so this method isn't
perfect. In fact, I can induce a several-minute error by slouching slightly
vs. standing up straight).
Even if it's not accurate enough for real navigation, it did serve its purpose
in giving me something to practice bringing
sights down with (and it's long
enough to be able to rock the sextant to find
true vertical). Now that I've got
that part down, time to work on improving the
accuracy with a real horizon.
:-)
--
GregR
--
GregR
