Next message: Frank Reed: "Re: Inflation ?????????????"
Joel Jacobs wrote:
"Take a proper Star scope and couple it with a small size horizon mirror,
and note the results at twilight."
I think this comment gets to the heart of the matter. In older sextants,
telescopes rarely had large apertures. They went for small aperture and long
focal length. The horizon mirror only needs to be as big as the aperture of the
telescope. Navy sextants from the Second World War had small horizon mirrors
because their telescopes were usually small in aperture. Naturally there is
no reason to have a horizon mirror bigger than than the telescope aperture.
And:
"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."
And that brings us to the index mirror. This doesn't need to be any wider
than the horizon mirror, but it helps a lot if it's longer (bigger in the
dimension along the index arm) because it will be foreshortened when the sextant
is set to a large angle. You can see this by setting the sextant to 120
degrees and then looking through the horizon glass at the index mirror.
-FER
42.0N 87.7W, or 41.4N 72.1W.
www.HistoricalAtlas.com/lunars
