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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Sextant Collimation Error
From: Frank Reed
Date: 2020 Jun 27, 21:52 -0700
From: Frank Reed
Date: 2020 Jun 27, 21:52 -0700
Early octants often had two sight peeps separated by 1-1.5 cm horizontally. A metal shade could slide over one or the other of them. This was equivalent to the riser on sextant scopes (both historically and today). The line of sight (line of collimation) was still expected to be parallel to the frame but at two different levels.
The small size of the peephole on early octants served as "poor man's eyeglasses". If you are somewhat near-sighted and normally wear glasses or contacts, try poking a small hole in a bit of cardstock, maybe 2-3 mm across, and look through it. Notice how your visual acuity greatly improves!
Frank Reed
