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Advice on Box Sextant
From: Geoffrey Kolbe
Date: 2016 Mar 31, 12:54 +0100
From: Geoffrey Kolbe
Date: 2016 Mar 31, 12:54 +0100
On 30 March 2016 at 16:28, Alexandre Eremenko <NoReply_Eremenko@fer3.com> wrote:
I own a very similar sextant, but made by Troughton and Simms. It works remarkably well, much better than one can expect.
That was my reaction too. I bought mine after you had said how impressed you were with yours.
The telescope is a Galileo one, and the telescope filter is lost. It has two index glass filters. The absence of the telescope filter prevents me from measuring Index error with the usual method using Sun. But all observations I took with it indicate that there is no perceptible index error.
The side error and the index error can be removed using the little key, the top of which is the smaller of the two knurled knobs on the top
In general, I find this telescope inconvenient (too small, too small field of view). For most observations I just do not use it. It does not seem to influence accuracy. The true purpose of Galileo telescope on a sextant is to collect more light in twilight observations. But this telescope has so small diameter that it is completely useless for this purpose. For sun observations is helps just a little.
I figured as much. I contemplated making a small telescope for this instrument - but the sextant really is very small and making a usable telescope on a suitable scale seems a lot more effort than the return would justify. A small slip-in filter holder is another matter though..... I will give that some serious thought.
Geoffrey Kolbe
