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Re: Suitable Sextants - Mirrors
From: Joel Jacobs
Date: 2005 Nov 18, 11:24 +0000

Hello George and Group,

From George Huxtable: "What's your estimate of the field of view of the scope, in degrees? And what's your estimate of the path length, in mm, between the objective of the scope and the mid-line of the horizon mirror, and the distance between the mid-lines of the two mirrors?"

I selected three instruments that were handy to me at home and not at our warehouse. This precluded having an Astra III B in the sample. These three are two sextants and one octant from different periods. A and B are separated by 27 years. The octant a is 230 years old. Each is from a different country. Names have been omitted, until George's analysis is complete.

Sextant A

Scope 4 x 40

Field of view 7.0 degrees
Index mirror, 57 x 42mm
Horizon Mirror, 57mm dia.

Distance OL - HM, 12.3mm

Distance IM - HM, 8mm

Sextant B

Scope 3.5 x 30

Field of view 8.0 degrees
Index mirror, 57 x 42mm
Horizon Mirror, 57mm dia.

Distance OL - HM, 10mm

Distance IM - HM, 8mm

Octant C

Scope None - Peep sight

Field of view, NA

Index mirror, 50 x 31 mm
Horizon Mirror, 24 x 20 mm

Distance OL - HM, 9mm

Distance IM - HM, 7mm

Thanks George,

Joel Jacobs

--
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http://www.landandseacollection.com

-------------- Original message from george huxtable <george@HUXTABLE.U-NET.COM>: --------------

> >Since I think you have a sincere interest in "knowledge" and enjoy sharing
> >your opinions in great detail with others,
>
> Thank you for the compliment, Joel ...
>
> >what I would like to learn from you is whether contemporary sextant's
> >mirror size and scopes are optimized. So you need not search for the
> >dimensions which are typical of most major brands they are:
> >
> >Scope 4 x 40
> >Index mirror, 57 x 42mm
> >Horizon Mirror, 57mm dia.
>
> Happy to give my opinion on that matter, Joel. I would just like some
> further information first, please, about your "typical" sextant. What's
> your estimate of the field of view of the scope,! in degrees? And what's
> your estimate of the path length, in mm, between the objective of the scope
> and the mid-line of the horizon mirror, and the distance between the
> mid-lines of the two mirrors?
>
> George.
>
>
> ===============================================================
> Contact George at george@huxtable.u-net.com ,or by phone +44 1865 820222,
> or from within UK 01865 820222.
> Or by post- George Huxtable, 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13
> 5HX, UK.

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