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Barlows and Image Amplifiers


Barlows and Image Amplifiers
Barlow lenses and image amplifiers are used to increase the effective focal length of a telescope. This results in more magnification. Barlows and image amplifiers are most commonly used in imaging applications, but they can also be used with eyepieces for visual observing. Some light transmission will be lost due to the added lenses and air to glass surfaces, therefore, we do not recommend these items for observing deep space objects.

Barlows and Image Amplifiers

Celestron Omni Barlow 2x
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$42.00
TeleVue 2x Barlow 1.25"
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$128.00
Celestron X-Cel LX Barlow 2x
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$84.00
TeleVue 3x Barlow 1.25"
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$128.00
Celestron X-Cel LX Barlow 3x
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$84.00
TeleVue 2x Big Barlow 2"
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$218.00

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TeleVue 2.5x Powermate 1.25"
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$218.00
TeleVue 5x Powermate 1.25"
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$205.00
TeleVue 2x Powermate 2"
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$327.00

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TeleVue 4x Powermate 2"
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$333.00

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Why should you consider using a Barlow?

Historically speaking, a Barlow was once the most practical means to achieve high magnification with a telescope. If we look back at the eyepieces that were available several decades ago the answer becomes immediately obvious. There was a time when all eyepieces were scaled designs where everything about them grew larger or smaller in concert with the focal length. Plossls are one of the few remaining popular scaled eyepiece. The eye relief of a Plossl eyepiece is 0.75x the focal length by design, therefore; an 8mm Plossl has only 6mm of eye relief. Plossl eyepieces with focal lengths shorter than 8mm are not very practical, which is why they are relatively uncommon. Using a Barlow circumvented the problem of limited eye relief when using scaled design eyepieces. Purchasing a Barlow can be an inexpensive means of doubling your eyepiece collection

How to choose a Barlow for Visual Use

Barlows are available in a variety of magnification factors, with 2X being by far the most common. We strongly recommend the 2X variety above all others for visual use. Why? Because having magnifications at your disposal separated by powers of two tends to be quite useful. In addition, the higher magnification factor Barlows tend to run into the wall of practical magnification with longer focal length eyepieces. Using a 2X Barlow with a 12mm eyepiece may be practical in a wide variety of telescopes, but the same cannot be said when combining that same eyepiece with a 3X Barlow.

How to choose a Barlow or Image Amplifier for Imaging Applications

Imagers are usually more concerned with field of view than magnification, with the notable exception of planetary imaging. There are a number of free tools available for calculating the true field for any combination of telescope and camera. We are rather fond of CCD Calc because it goes beyond the basic mathematics and provides actual overlay views of the net result on a number of the common showpiece astronomical objects. When using such a program, simply enter the magnification factor into the "Barlow or reducer" data field.

Planetary imaging usually requires a lot of effective focal length, and the use of 3-5X magnification factor is common for this application. In most cases a planet will still be small relative to the actual field of the camera, and the difference between a Barlow and image amplifier is less likely to be seen. Barlows produce diverging light rays whereas a high quality image amplifier like the TeleVue Powermate produce parallel light rays. The TeleVue Powermate is the preferred approach for imaging larger targets, particularly when using cameras with larger sensors.