Next message: Bill: "Re: Suitable Sextants - Mirrors"
Joel Jacobs wrote:
"Your analysis though interesting, fails to take into account that a
sextant's mirrors are not used in a static state, and hence size does make
a
difference. Consider that the platform is moving directionally, and rolling
and
pitching all at the same time."
Frank wrote:
But since the mirrors, telescope, and other components of the sextant are
all experiencing the same motion, this really isn't relevant to mirror
size.
They're either big enough to fill the field of view, or they're not --no
matter
how much pitching and rolling there is.
My reply:
In my experience taking onboard cuts in all types of conditions with many
different models of sextants I stand with what Joel states just from a
practical use stand point. I've taken sights with old(WWII vintage)David
White sextants that had the smaller mirrors than the sextants of today and
it is more difficult to hold the body in the mirrors with the smaller
mirrors. Granted those same sextants had the old type scopes on them also.
It is sooooooo much easier to do the work with a modern sextant that has the
larger mirrors and larger lens on the scopes.
As for plastic sextants:
I wouldn't use them for serious, everyday onboard work because of just the
following 2 reasons.
1. The optics are horrible. Period. Even on the top of the line Davis 25's
the optics don't even compare with the optics on a used Astra. Even on an
Astra's worst day there is no comparison.
2. While running around taking care of duties etc one doesn't have time to
sit and futz with a plastic sextant's idiosyncrasies and take multiple cuts
for averaging while underway.
One gets out on the wing, takes the cut (experience will let you know if the
cut feels right), record the data, reduce for pos and go on about one's
duties.
Now, if all one has is a plastic sextant to use........ by all means use it.
Heft:
I like to use the heavier sextant. Just like I like to use a heavier rifle.
The heavier sextant feels more stable, even in the roughest seas, than a
light instrument does. One has to learn how to spend the time to set up a
shot and then take that shot accurately and quickly. The important step here
is the set up almost more so than the shot itself. After everything is set
up for the shot and the cut/shot is taken within the time frame, known by
the observer from experience, to be within his/her limits of physical
comfort a metal sextant isn't heavy at all. It's like an extension of one's
body even in a pitching, bucking little vessel.
It's good to be back with you people after a few months working the shipping
lanes of the Pacific and Indian Oceans.
