NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Advice concerning sextants
From: Jeremy C
Date: 2010 Feb 23, 12:00 EST
From: Jeremy C
Date: 2010 Feb 23, 12:00 EST
I have used both types of mirrors and much depends on the telescope I'm
using. When using a lower powered scope (say 4x and less) I much prefer
the whole horizon mirror. I am generally annoyed by the body disappearing
as I am rocking it and find it much easier to find the nadir with a
whole-horizon mirror. I also find it easier to find the stars on the whole
horizon mirror. As mentioned, there is trouble with dimmer horizons, as
there is a loss of light and contrast, but I've never had a problem getting
a round of sights in with the whole-horizon mirror.
When I use my 7x scope, the effect is that the half-horizon mirror acts
like a whole horizon mirror with none of the light loss. I find this an
idea solution. This is the combination I use on the ship. I have
tried with the lower powered scope on the same sextant and have not been as
happy.
As usual, choosing a sextant configuration is mostly a matter of the
circumstances you are going use it as well as preference. Since I am using
it on a large ship that is relatively stable, I can get away with high powered
scopes and lower light transmission of whole horizon mirrors. The needs
for small boat or land based sextant use are far different.
Jeremy
In a message dated 2/23/2010 12:42:56 A.M. Eastern Standard Time,
jn.wilson@juno.com writes:
John reminds me of my first experience with the whole horizon sextant
mirror, which I called the half silvered mirror, was that finding the
horizon in dim light was difficult. I found no advantages, in that the
sun and moon images can be seen in the clear part of the mirror, aiding
in bringing them down.
Now, if someone would make a horizon mirror that was half silvered on
only the left side, that might be worth something. But I might still have
the same problem at twilight, where I need all the light available to see
the horizon.
I'm sure that the article mentioned noted that half silvered mirrors (one
way glass) allow only a portion of the light to pass. When we remodeled
our bath, we had one installed in our shower for privacy. The room was
significantly darkened, and plants wouldn't grow. The amount of light
reduction is significant.
Jim Wilson
____________________________________________________________
Nutrition
Improve your career health. Click now to study
Get a NavList ID Code
A NavList ID Code guarantees your identity in NavList posts and allows faster posting of messages.