A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Bill Morris
Date: 2021 Apr 23, 21:00 -0700
A biconcave simple lens of the correct(negative) focal length will do. A good source is surplushed.com The negative ratio of the focal length of the objective lens(which should be positive achromat) to the eye lens gives the magnification. e.g. f/l objective lens +75 mm, f/l eye lens -25 mm, magnification = 75/25 = x 3. The length will be 75 - 25 = 50 mm.