| Barlows |
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Concept: I originally designed the Tele Vue Barlow line to complement the high performance of our eyepieces. Only 2 elements of high index glass were
required to reduce all aberrations to well below the airy disc in an f/4 system. It has taken a good 15 years, but I think we're finally laying to rest the popular myth of the "degrading
Barlow."
In a 1997 Sky & Telescope review, Terrence Dickenson wrote "...Technology has erased the old objections. A modern Barlow will not degrade your telescope's optics. Anyone telling you otherwise is using outdated information. Moreover, the highly regarded Nagler eyepieces and their clones have built-in
Barlows - ample evidence that the lens is not some detrimental intruder." Thanx
Terry, I couldn't agree more - Al Nagler |
Properly designed Barlows do wonderful things: They amplify power, slow the telescope’s f/# (improving eyepiece sharpness), and give designers the opportunity to compensate for eyepiece aberrations.
Tele Vue Barlows use multi-coated high index glasses for optimum aberration correction, exceptional contrast with virtually no light loss. Observed performance is aberration free, even when tested with f/4 scopes. They even improve our competitor’s eyepieces and telescopes!
Tele Vue Quality
Compromise image quality in any part of the optical chain and you've compromised every part! Tele Vue product design and execution deliver consummate satisfaction. Every Tele Vue Barlow must pass the same rigorous f/4, full field testing as all our eyepieces. All Tele Vue Barlows now use brass clamp rings for secure, non marring holding of eyepieces and accessories.
Barlow Magnification Chart for Imagers
For astro-imagers, the above chart indicates the magnification for each Barlow (2x, 2x Big & 3x) as a function of distance from the Barlow top surface to the imaging surface (CCD or film).
1¼" Barlows
Offered in 2x and 3x magnifications, these 1¼" Barlows perform identically. Simply choose either or both based on your eyepiece collection. Features include parfocal-ization, 1¼" filter threads, captive lock screws that won't fall out and full multicoatings.
2" Big Barlow
Offered in a 2x magnification, the Big Barlow is ideal for Newtonian scope owners. It will be parfocal with both 2" and 1¼" eyepieces in this application. Features include threads for 48mm filters, captive lock screw and full multi-coatings.
Barlow Interface
You can double the power of any
eyepiece with the 2x Big Barlow, but adding the interface lens brings the pupil back
to original position when used with long focal length eyepieces such as the
Panoptic 41, 35, or 27mm 2" models. The combination of interface and Big
Barlow mimics the Powermate concept.
Note: The Big Barlow is not recommended for use with 2" diagonals because it's length prevents it from being parfocal. With some telescopes, focus might not be reached, particularly when the interface lens is also used with it. A far better approach with no potential problems in any scope or with any eyepieces is to use the 2" 2x Powermate (PMT-2200), which essentially includes the interface function. See the write-up on Powermates for more details.
User Reports
“Tele Vue's Big Barlow doubled the power but, like an optically perfect window, never gave any other indication that it was in the light path. The airy disc and surrounding diffraction rings were perfect, with no sign of astigmatism or coma. It will provide outstanding optical performance with all your eyepieces.”
— Alan Dyer
Astronomy Magazine
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