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I own a very similar sextant, but made by Troughton and Simms.
It works remarkably well, much better than one can expect.

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.

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 was even able to take back sights with this sextant.
It has the scale of 150 degrees.

Alex.

________________________________________
From: NavList@fer3.com [NavList@fer3.com] on behalf of Sean C [NoReply_SeanC@fer3.com]
Sent: Wednesday, March 30, 2016 10:03 AM
To: eremenko@math.purdue.edu
Subject: [NavList] Re: Advice on Box Sextant

Geoffrey,

The sextant is supposed to arrive some time between April 7th and 15th. I will 
try to answer your questions once I have it in my hands. I'm by no means an 
expert, though, and I'm not exactly sure how to determine the magnification 
power of the telescope - or what kind of material is used in the filter. I 
suspect it's intended purpose is only to reduce glare from the horizon. 
Obviously, I should be able to tell whether the telescope is Galilean or 
inverting.

Perhaps I will install the filter and try viewing the sun through 
progressively fewer shades on my Astra until I can determine whether it is 
safe to use for index error checks by itself.

Regards,

Sean C.

   

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