Re: US Navy and celestial...
From: Greg Rudzinski
Date: 2017 Sep 15, 16:56 -0700
Image 1. No sun filters shading the index mirror would suggest a high altitude moon observation.
(US Navy MK 3 with split horizon mirror)
Image 2. No sun filters shading the index mirror with index arm at or near zero would indicate an index error check using the horizon.
(Cassens & Plath with whole horizon mirror)
Image 3. Sun filters shading the index mirror with index arm near zero would indicate a low altitude observation of the Sun.
(Astra lllB with split horizon mirror)
As long as the bridge glass is flat there shouldn't be a refraction problem. No worse than stacking filters.
From: Dustin Baenen
Date: 2017 Sep 15, 14:59 -0700
I notice the last two pictures posted show sextants being used from the interior of the ship shooting "sights" through glass windows. I would think that the glass would create some kind of extra refraction error or perhaps just an abboration leading to reduced accuracy. I have no evidence to support this hypothosis, just seemd like "common sense". I assume these navigators were demonstrating the use of the sextant (the second photo shows the gentleman taking a sight with the index arm right around zero) for the photographer. Can someone please confirm this thought or set me straght? Is it ok to sight through a glass window? On my Davis AH there is two panes of glass that the light passes through before hitting the sextant but because they are at complimentary angles I assumed this cancled out any error the glass might produce. Im sorry that this was slightly off topic to the thread but it made me wonder.