NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: UNK
Date: 2013 Dec 20, 09:27 -0800
The "outside in the sun" folks were correct. the focal length of the objective lens is 150 mm and Yes, I wear glasses. After thinking all of this through, I sketched out and attached where I think I am.
3 X erect scope.
150 mm focal length of the objective lens.
110 length of the main body of the scope.
The eyepiece lens should have a focal length of about -50 mm.
The lenses should be arranged with the 150 - 50 or about 100 mm apart.
At the 100 mm mark, the rays from the objective lens will be about 6 mm across.
The eyepiece holder/sliding tube has a 7 mm aperture towards the objective lens.
The best choices from Surplus Shed seems to be a DCV (Double Concave) lens of 10.9 mm x -52 or a 6.77 x -49. There are ACH (Achromatic) lenses available of 9.5 x -49 and 7.0 x -45. The ACH 9.5 x -49 seems like the best choice. For $4 to $7 each, I'll probably get an assortment.
Comments are welcome.
Regards, Noell
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