The unilens monocular is a simple refracting telescope for field use, designed by Major Baden-Powell, F.R.A.S.. Consisting of only one lens, it is the simplest of all telescopes, and while occupying v

In geometrical optics, a focus, also called an image point, is a point where light rays originating from a point on an object converge. Although the focus is conceptually a point, physically the focus