What is a Barlow Lens?

March 26, 2018

A Barlow lens is an optical device that magnifies the image seen through your telescope. It’s essentially a negative lens (or concave lens) that works by diverging the light entering your telescope, which increases the effective focal length of your telescope. This results in a higher magnification using the same eyepiece.

 

In simpler terms: A Barlow lens allows you to double or triple the magnification of your current eyepiece by increasing the focal length of your telescope. So, instead of buying multiple eyepieces with different magnifications, you can achieve a broader range of magnifications with just one Barlow lens.

 

How Does a Barlow Lens Work?

To understand how a Barlow lens works, let’s look at the basics of telescope magnification. Magnification is determined by dividing the focal length of your telescope by the focal length of your eyepiece. For this example we will use the NexStar 5SE with its 25mm eyepiece:

Now, when you add a Barlow lens, it multiplies the effective focal length of your telescope. For example, if you have a 2x Barlow lens, it doubles the focal length, so your telescope will now behave as if it has a 100mm focal length.

Use Within Your Telescope’s Limits: Before using a Barlow lens, check your telescope’s highest and lowest useful magnification to avoid over- or under-powering your view. For best results, pair the Barlow with medium- to low-power eyepieces (like 25mm or 15mm). Going beyond your scope’s limits—especially with high-power eyepieces—can lead to blurry or distorted images, particularly under poor atmospheric conditions.

 

Types of Barlow Lenses

  1. 1.5x Barlow Lens: A moderate magnification boost, often used when you don’t need extreme magnification but want a little more detail.
  2. 2x Barlow Lens: The most common type, providing a solid magnification boost that works well for most amateur astronomers.
  3. 3x Barlow Lens: For higher magnification, useful for viewing planets and other details that require more power.

 

How to Use a Barlow Lens:

Using a Barlow lens is simple! Here’s a step-by-step guide:

  1. Choose Your Barlow Lens based on the magnification you need.
  2. Insert the Barlow Lens into the focuser or the diagonal, depending on your setup
  3. Insert Your Eyepiece into the Barlow lens.
  4. Focus your telescope as you normally would before you observe.

 

Spotlight: Luminos Barlow Lens

If you're looking for versatility, the Celestron Luminos Barlow Lens stands out. It features a 2" barrel but includes a removable adapter that allows it to accept both 2" and 1.25" eyepieces. This dual compatibility makes it a great choice for observers who want to expand their magnification options without being limited by eyepiece size. Plus, its fully multi-coated optics and machined aluminum body ensure bright, sharp views across the field.

 

A Barlow lens is a must-have accessory for any astronomer who wants to enhance their magnification capabilities without investing in numerous eyepieces. It’s simple to use, versatile, and affordable, making it an excellent addition to your astrophotography or stargazing kit. Whether you’re peering at planets, lunar craters, or distant stars, a Barlow lens can help you zoom in on the wonders of the universe with ease.