NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Suitable Sextants
From: Joel Jacobs
Date: 2005 Oct 11, 17:56 +0000
From: Joel Jacobs
Date: 2005 Oct 11, 17:56 +0000
Hello Alex,
Large mirrors collect more light and transmit more though the optics which are an advantage in taking twilight sights.
The second adavantage is that celestial objects tend to move around on the horizon mirror due to the motion of the vessel or of the sight taker. They also seem to move more when taking high altitude sights. The larger size mirrors provide more surface area for the body to dance on before being lost from view.
Also try WD 40, a moisture displacement chemical, to minimize affects of spray.
Joel
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-------------- Original message from Alexandre E Eremenko <eremenko@MATH.PURDUE.EDU>: --------------
> Dear Joel,
>
> > 1. The larger the size of the mirrors, the better.
>
> I always read and hear this, but I am not sure that
> I understand exactly why the larger mirrors are better.
> Can you explain?
>
> > 2. Sextants with enclosed tangent screws
> > are prone to having them freeze
> > unless they are cleaned after use when
> > there is spray.
>
> This I confirm, even with my small experience.
> The remedy is to wash it with fresh water after
> a spray. And the fresh water is sometimes scarce
> on a small boat.
>
> Alex.
