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Re: Kelvin Hughes Sextant
From: Brad Morris
Date: 2014 Nov 18, 13:27 -0500
From: Brad Morris
Date: 2014 Nov 18, 13:27 -0500
Hello Fred
The primary use of the wires in the scopes was to insure that tangency of the images occurred in the center of the field of view. For the tic-tac-toe lines, you would want to be within the center square. For the two parallel lines, you want to be between the lines and still centered.
When doing so, the measurement is "more accurate" and does not suffer from collimation errors.
I'll leave it to the others to more accurately describe how being away from the center of the FOV affects the measurement. I'm sure there is an equation.
Brad
On Nov 18, 2014 11:47 AM, "Fred Hebard" <NoReply_Hebard@fer3.com> wrote:
Jerry, Thank you for posting the photos. That is a Husun or Hughes sextant. They merged with Kelvin soon after WWII. The serial number on the index arm is not a Hughes serial number, which threw me off. The Hughes serial number was often stamped in the arc. That could be clarified if you post a photo of the certificate in the top of the box. For the certificate in the box top, it also will be interesting to compare the arc deviations to those on the certificate illustrated in David Morris' post. Note there are no arc errors whatsoever in David's certificate. That was typical of Hughes sextants until WWII, when they started tolerating errors of up to a minute of arc. However, for WWII, they concentrated on volume production; the serial numbers increased from 23,000 to 50,000 between 1939 and 1945. They had started from 1 in the 1800s. Hughes also concentrated on producing the three-ring "Mate" model sextant during the war, which has a 6" arc, not as accurate as the larger open frame in your instrument and the one illustrated in David's link. I would not be surprised if they had spent more time perfecting the arc for your model, which would be revealed by the certificate photo. The two shades fit over the ends of the telescope eyepieces. They are very handy for use with an artificial horizon. The two eyepiece shades are for the inverting scope, as you describe. There should be another installed in the star scope (short fat telescope), which also should accommodate the shades. The star scope is installed backwards in photo f12-image. I would be interested in hearing for what the wires in the inverting telescope eyepieces were used. Regards, Fred Hebard mbiew---.net On Nov 17, 2014, at 5:46 PM, Jerry Gorman wrote: > Attached photos to clarify previous post > > > > Attached File: > > (f11-image.jpg: Open and save) > > Attached File: > > (f12-image.jpg: Open and save) > > Attached File: > > (f13-image.jpg: Open and save) > > >
