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 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.
===============

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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