A Barlow lens is a diverging lens, placed in front of the focal point of a
telescope, that increases both magnification and eye relief when used in conjunction
with an eyepiece. The magnification is
typically doubled, though at the cost of a fainter image. Invented in 1834
by the English engineer and mathematician Peter Barlow (1776–1862), the lens is used commonly by amateur astronomers.
AND OPTICAL PHENOMENA
EQUIPMENT AND TECHNIQUES