What is a Barlow Lens? Choosing the right one.

by: OZScopes - The Australian Telescope Experts

Barlow lenses are a cost effective way of increasing telescope magnification. The standard Barlow lens has 2x magnification, and will connect directly to your eyepiece. There is also 3x Barlow Lens, although unlike the 2x Barlow lens, this more powerful lens may not be as compatible with all telescopes.

Generally, although Barlow lenses are a great, affordable way to extend your eyepiece collection, you will find that the images you'll get with one will be slightly degraded. Image quality degrades with use of a Barlow lens because it adds another layer of glass for light to pass through, which thus provides it with more resistance in obstructing the light.

If you were after the best views possible, you'll get them by purchasing a new eyepiece with extra low dispersion (ED) glass. ED glass does away with what's called chromatic abberration - a distortion in the image when looking at very bright images, where lines are blurred with small spectrums of light.

Every amateur astronomer should consider the Barlow lens as an extremely useful tool. One of the greatest advantages of say, a 2x Barlow Lens is that it doubles the magnification of your eyepieces, which can also be effectively seen as doubling your eyepiece collection. For example, adding a 2x Barlow to your collection of a 32mm, 26mm and 10mm eyepiece would be like make your collection contain a 32mm, 16mm, 26mm, 13mm, 10mm and 5mm eyepiece. So you are essentially getting three new eyepieces for the price of one!

Choosing a Barlow Lens
When selecting, it is critical that you choose one with a barrel size that will fit the eyepieces you have. The barrel size is the diameter of the eyepiece tube that fits into the focuser. Standard eyepiece barrel sizes range from 1 to ¼inches. Some eyepieces may use a larger 2inch format while others from the more inexpensive telescope range may use smaller 0.965inch formats.

Using a Barlow Lens
Using the Barlow Lens is easy. Instead of dropping the eyepiece into the focuser, you first have to drop in the Barlow lens, then connect your eyepiece to the Barlow.

See OZScopes' range of Barlow Lenses