Barlow Lenses and Focal Reducers

Simply, it's a concave (negative) lens placed between a telescope objective and eyepiece to increase the magnification, usually by two or three times. The negative lens reduces the angle of convergence of the light cone, effectively making it appear to the eyepiece that the primary has a longer focal length. It was invented in the early1800s by English physicist Peter Barlow (1776–1872)

Telescope Accessories for beginners

There are some essential accessories and gadgets that you should consider buying with your telescope.