TELRAD Telescope Reflex Sight with Mounting Base
The Zhumell 2” ED Barlow Lens doubles the magnification of any 2” or 1.25” eyepiece, giving you the most bang for your buck of any telescope accessory on the market!
Extra low dispersion glass for sharper, high contrast views
The Zhumell 2X ED Barlow Lens was manufactured with extra low dispersion glass. ED glass is more expensive, but since it helps light rays of different colors focus at the same point, the result is sharper, higher contrast results.
Comes with an adapter for your 1.25” eyepieces
The Zhumell 2X Barlow comes with a 1.25” compression ring adapter. This means you can use your 2” eyepieces AND your 1.25” eyepieces in the same Barlow, saving you money.
A bit more about Barlows
A Barlow lens is designed to multiply the magnification of any like-sized eyepiece. While a 2X Barlow is the most common, you can find Barlows of other magnification ratios as well, including 2.5X, 3X and even 5X. Simply insert the chrome barrel of the Barlow into your telescope’s focuser or diagonal, and then insert your eyepiece of choice into the top of the Barlow.
How do I calculate magnification?
To calculate the power of an eyepiece when inserted in your telescope, you need to divide the focal length of the eyepiece—the number is almost always etched on the eyepiece—into the focal length of your telescope. The focal length of your telescope is always a big number designated in millimeters. If you can’t find it marked on your telescope, look at your instruction manual under specifications for this information.
Example: An 18mm eyepiece used in a telescope with a focal length of 1000mm has a magnification of 180X (1000 divided by 18 = 180). When you use your 18mm eyepiece in a 2X Barlow, you will achieve a magnification of 360X.
When choosing an eyepiece for your telescope or an eyepiece/Barlow combination, you will need to take the resulting magnification in mind. The maximum magnification one can use on a telescope depends on the aperture of the telescope as well as the current seeing conditions from your observing location.
How do I know if I’ve reach maximum magnification?
The best way to observe is to start out with a low power eyepiece—the higher the number on the eyepiece, the lower the magnification—and work your way up. When you reach the point where you can no longer achieve sharp focus, you’ll know you’ve surpassed your maximum magnification for the evening.
It is nice keep a list of your magnification choices, with and without a Barlow, close at hand. If your 20mm eyepiece gets sharp results but placing it in a Barlow results in a blurry image, then you will know that a 10mm eyepiece—the result of a 20mm in a 2X Barlow)—is too much. Try a magnification that is one step down from that of the 20mm/Barlow combination and and see if that will do the trick. Before long, you’ll know your telescope’s capabilities from your favorite observing sites without much, if any, experimentation, but always be on the lookout for an out-of-the-ordinary, superb night of seeing! Those nights are magic, and you’ll want to be out as long as possible to see just how far you can push your telescope. Welcome to the world of the amateur astronomer!
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Telescope Accessories Series
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