{"id":27746,"date":"2022-01-05T20:04:50","date_gmt":"2022-01-05T20:04:50","guid":{"rendered":"https:\/\/www.skyatnightmagazine.com\/?p=46254"},"modified":"2022-01-05T20:16:13","modified_gmt":"2022-01-05T20:16:13","slug":"what-is-a-barlow-lens","status":"publish","type":"rss_feed","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/rss_feed\/what-is-a-barlow-lens\/","title":{"rendered":"What is a Barlow lens?"},"content":{"rendered":"

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By Steve Richards\n \t\t<\/p>

Published: Wednesday, 05 January 2022 at 12:00 am<\/p>

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A Barlow lens is an optical tube containing lens elements that diverge the light passing through them.<\/p>\n

Named after English physicist and mathematician Peter Barlow, Barlow lenses add a second lot of magnification to each of your eyepieces<\/a> while maintaining the existing eye relief.<\/p>\n

The Barlow lens is an optical tube containing lens elements that diverge light passing through.<\/p>\n

If one is inserted into the light path of any type of scope, the effective focal length of the scope is increased.<\/span><\/p>\n

You calculate the magnification<\/span> of a telescope by dividing its focal length by the focal length of the eyepiece.<\/p>\n

Therefore, an increase in the effective focal length of the telescope results in an increase in magnification.<\/p>\n

For example, this means a 17mm eyepiece will behave like a 5.6mm eyepiece. As a bonus, the increase in the scope\u2019s focal ratio can improve image sharpness, but only under ideal conditions.<\/span><\/p>\n

Inserting a Barlow lens into the light path of any type of telescope increases the effective focal length, usually by doubling it, although some designs have an even greater effect.<\/p>\n

Using a Barlow lens effectively doubles the number of eyepieces that you have in your collection.<\/p>\n

Barlow vs Powermate: what\u2019s the difference?\u00a0<\/strong><\/h2>\n
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Both Barlow lenses and Powermates act as image amplifiers by increasing the effective focal length of your telescope, thereby increasing the magnification achieved with any eyepiece.<\/span><\/p>\n

Typical Barlows have a magnification of 2x and are composed of two or sometimes <\/span>three elements in a single group, forming <\/span>a negative lens.<\/span><\/p>\n

This lens produces a diverging ray of light which, as well as magnifying the view, moves <\/span>the eyepiece\u2019s exit pupil farther outwards,<\/span> thereby increasing the eye relief.<\/span><\/p>\n

This effect is not too noticeable with short to medium focal length eyepieces, but it is more significant in longer focal length eyepieces as it can lead to vignetting if the eyepiece lenses aren\u2019t wide enough to let the full width of the altered light cone through.<\/span><\/p>\n

Eyepiece to Barlow lens spacing has a significant effect on the magnification achieved.<\/span><\/p>\n

A Powermate is a telecentric design with four lenses in two doublet groups: a smaller negative lens and a larger positive lens arranged so that light exits the Powermate in parallel rays.<\/span><\/p>\n

This design ensures that the original eye relief of the eyepiece remains unchanged, making it more suitable for longer focal length eyepieces and avoiding the risk of vignetting.<\/span><\/p>\n

A Powermate\u2019s magnification remains fairly constant irrespective of where the eyepiece is positioned.<\/span><\/p>\n

From a lunar and planetary imaging point of view, Powermates are the better choice as they can be stacked<\/a> to produce high levels of magnification.<\/span><\/p>\n

7 of the best Barlow lenses<\/strong><\/h2>\n
1<\/span>

Celestron X-CEL LX 3x Barlow<\/h3>\n<\/div>

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Celestron\u2019s X-CEL LX 3x Barlow is designed to be the perfect companion to the company\u2019s range of X-Cel LX eyepieces, with a matching rubber grip pattern, copper-coloured banding and an all black silk finish.<\/p>\n

The fully multicoated, three-element design is the second lightest in this group at 142g, and the lens is the second smallest in terms of length, but it has a solid, well constructed feel to it that gives plenty of confidence in use.<\/p>\n

The eyepiece barrel has a plain profile, which makes inserting it into a star diagonal<\/a> a quick process indeed.<\/p>\n

Its anti-marring brass compression ring is smooth and the internal micro-baffles, finished in a matt black, complete a well-thought-out design.<\/p>\n

Views of Venus were excellent, and on the Moon plenty of sharp detail was visible. We very much enjoyed the view of the Orion Nebula\u2019s Trapezium stars, which were very sharp and clear.<\/p>\n