NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Suitable Sextants
From: Alexandre Eremenko
Date: 2005 Oct 11, 18:05 -0500
From: Alexandre Eremenko
Date: 2005 Oct 11, 18:05 -0500
Joel, Yes, you are right. Most of my experience was from land. And on a small boat (not so small, 42 feet) at first I could not use any scope at all, just had to do it without scope (and with poor results). A. On Tue, 11 Oct 2005 joel-jacobs@att.net wrote: > Alex, > > Sometimes the proof of the pudding is in the eating. > > Take a proper Star scope and couple it with a small size horizon mirror, and note the results at twilight. > > Also take a sextant with small mirrors and use what ever scope you are most comforatble with and try some high altitude sun sights. Note the results. > > I suggest it will be like your use of an inverting scope on land vis-a-vis at sea. > > You never notice the difference until you're at sea. > > Joel > > -- > Visit our website > http://www.landandseacollection.com > > > > > -------------- Original message from Alexandre E Eremenko: -------------- > > > > Joel, > > Thanks. It seems to me that in both cases it is the > > diameter of the telescope objective lens that is most relevant. > > Provided that the mirror occupies the whole field of view. > > Indeed, once this is the case, > > increased mirror will not send more light > > into the scope. Same about motion. > > > > So you probably mean that in the old sextants with small mirrors > > the mirrors did not occupy the full field of view, > > and some of this field of view was thus wasted, correct? > > > > Alex. > > > > > > On Tue, 11 Oct 2005 joel-jacobs@att.net wrote: > > > > > 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 > > > -- > > > Visit our website > > > http://www.landandseacollection.com > > > > > > > > > > > > > > > -------------- Original message from Alexandre E Eremenko > > : -------------- > > > > > > > > > > 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. > >