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From: George Huxtable (no email)
Date: Mon Aug 02 2004 - 05:40:00 EDT
Joel Jacobs <> wrote:
>From my experience, if your going to do serious navigation relying on
> twilight sights, the 7/8 scale sextants are very lacking. Their optics are
> not very good, and there small size mirrors are not anywhere as effective
> when taking star sights or high altitude sun sights.
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Something about that puzzles me. Why should it be so, I ask?
First, I should make it clear that I have never even handled such a 7/8
size sextant; and that observations on my own small boat have never passed
beyond a plastic job, though I have used many "posh" sextants, belonging to
others. So I make no claims to being an expert on sextants.
Yet, it seems to me that if you were to shrink a sextant to 7/8 of its
original size, and shrink its mirrors correspondingly (in both directions)
while preserving the same angular field-of-view of its telescope, then
(because the distance from the eye to those mirrors is also reduced to 7/8)
the patch of sky that the mirrors subtend would be exactly the same as
before.
So, in those circumstances, why should the smaller mirrors present any
disadvantage?
George.
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contact George Huxtable by email at , by phone at
01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy
Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
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