Barlows & Extenders

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A Barlow is a negative or diverging lens tube that finds its home in a telescope's focuser before adding an eyepiece. At one end of the tube is a concave lens that increases the telescope's effective focal length, which boosts the magnification power of the eyepiece by anywhere from 2X to 5 X, depending on the Barlow you choose.  The eyepiece is then inserted in the open tube end of the Barlow and is held securely in place by screws.  This is an easy way to expand your eyepiece selection’s magnification range, expecially if you have a collection of eyepieces with shorter eye relief, like standard Plossls or Orthoscopics.


How is a Powermate different from a Barlow?   While Barlows work very well for many applications, they are limited due to the fact that the negative lens used in their design increases the eye relief of the barlow/eyepiece combination.  In eyepieces with short eye relief this is generally not an issue, but with long eye relief eyepieces (desirable for comfortable views, especially while wearing eyeglasses), the eye relief can be pushed beyond what was intended by the eyepiece designer and cause vignetting of the image.  Powermates utilize a negative doublet plus a positive pupil-correcting doublet and are therefore able to achieve pure image amplification without the short-comings of a standard Barlow.  In other words, they leave the eye relief where it was intended to be.  Available in 1.25” and 2” models Powermates are offered in a range between 2x and 5x, and though they are an excellent choice for eyepieces with long eye relief they pair well with any eyepiece in your arsenal.

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