NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Paul Dolkas
Date: 2013 Dec 22, 20:55 -0800
Diopter is the reciprocal of focal length, measured in meters. 5 diopter is 1/5 meter, or 20mm focal length.
Paul Dolkas
From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf Of Noell Wilson
Sent: Thursday, December 19, 2013 10:31 AM
To: paul@dolkas.net
Subject: [NavList] Re: Inverting telescope for sextant
Thanks Alex,
My question would be what is the 130 mm which I see as the maximum distance where I get a sharp image looking through the objective lens? Can that reliably be treated as the focal length of that lens? If so, things fall into place.
Surplus Shed lists lens by type, diameter, and focal length. No diopters. The ID of the lens holder is 18.2 mm. They have a Plano Concave of 12.5 mm & -43 and other PCV’s and DCV’s that range from 15 to 17 mm and -33 to -39 f. No exact 18.2 & -43 but close enough.
Regards, Noell
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