A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Andrew Nikitin
Date: 2016 Oct 28, 11:02 -0700
> Google “plano convex plastic lens”
That might be an overkill as it brings precision lenses at significant price. Try "Bar magnifier" instead. It would find something like this $3 unit which you can scratch a hairline on and cut to right length.