Binoculars range (distance to an object)

Description

Binoculars, field glasses or binocular telescopes are a pair of identical or mirror-symmetrical telescopes mounted side-by-side and aligned to point accurately in the same direction, allowing the viewer to use both eyes (binocular vision) when viewing distant objects. Many binoculars have range finding reticle (scale) superimposed upon the view. This scale allows the distance to the object to be estimated if the object’s height is known (or estimable).
The common mariner 7×50 binoculars have these scales with the angle between marks equal to 5 mil. (One mil is equivalent to the angle between the top and bottom of an object one meter in height at a distance of 1000 meters -approximately the same size as a trigonometric milliradian)
e.g With the typical 5 mil scale (each mark is 5 mil), a lighthouse that is 3 marks high that is known to be 120 meters tall is 8000 meters distance.