Using a Barlow Lens

A cost effective way to increase the magnification of your eyepieces.

An extremely useful tool every amateur astronomer should have is a Barlow Lens. The Barlow lens was invented by Peter Barlow (1776-1862) an English writer on pure and applied mathematics. A Barlow lens is a concave lens that when placed between a telescopes objective lens or mirror and the eyepiece, will increase the magnification of the telescope.

A Barlow lens will connect directly to your eyepiece. The most common Barlow is the 2x Barlow. A 2x Barlow will double the magnification of the eyepiece it is attached to.? For example, if you were using a 20mm eyepiece on a telescope with a 1000mm focal length, you would have 50x magnification. If you attach a 2x Barlow lens to that eyepiece you will double the effective magnification of that eyepiece to 100x.

One of the greatest advantages of a Barlow lens is that it not only will double the magnification it will effectively double your eyepiece collection! If you had a 32mm 26mm and 10mm for example, adding a 2x Barlow would be like owning a 32mm 26mm 16mm 13mm and 5mm. A Barlow is much more cost effective, as it is usually less than the price of 1 eyepiece! 

Choosing a Barlow Lens

When selecting a Barlow lens it is critical that you select one with a barrel size that will fit the eyepieces you are going to use it with. The barrel size is the diameter of the eyepiece tube that fits into the focuser. The standard eyepiece barrel size is 1-1/4 Inches.? Some eyepieces use the larger 2-inch format and some really inexpensive telescopes use the smaller 0.965" format.? It is important that your Barlow lens has the same barrel size as the eyepiece you are going to connect it to.

Barlow lenses are offered in different magnifications. The most common is 2x.? This means it will double the magnification of any eyepiece it is connected to. There are also 3x or higher Barlow lenses. We recommend the standard and most common 2x Barlow lens for most users. The more powerful Barlow's may not work well with all telescopes.

Using a Barlow Lens

A Barlow lens is very simple to use. Instead of dropping the eyepiece into the focuser, you will first drop in the Barlow lens, then your eyepiece will connect to your Barlow.