Focal Length Adapters (Barlows)

Barlow lenses are used to change the magnification of an eyepiece.  If an eyepiece gives a magnification of 50x (e.g. 20mm eyepiece used with a telescope with 1000mm focal length), then the same eyepiece used with a 3x Barlow lens on the same telescope will give a magnification of 150x (3x50).  A Barlow lens effectively increases the telescope's focal length.  In the example above, the telescope has an effective focal length of 3x 1000mm = 3000mm.  Used with a 20mm eyepiece gives a magnification of 3000/20 = 150x.  The following product ranges form part of this category:

  • Barlow lenses:  These lenses are normally associated with additional magnification.  Thus, the magnification value is greater than one.
  • Focal reducers:  These lenses reduces the magnification for an eyepiece.  These lenses are primarily used for imaging (photography) and allows a larger field field of view to be imaged.  The reduction value is smaller than one and effectively reduces the telescope's focal length.
  • Coma correctors:  Fast (short focal length) Newtonians are prone to coma.  This is an optical effect where objects towards the edge of the image are out of focus and appears cometlike.  These lenses correct for this effect and allows reduced coma or even coma free wide field images.  These lenses typically comes with minimal added magnification and are therefor included in this category. 

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