Tele Vue 2" 2x Big Barlow with 1.25" Adapter # BWC-2211
"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 Anyone telling you otherwise is using outdated information.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." Thanks 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 their 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 their eyepieces. All Tele Vue Barlows now use brass clamp rings for secure, non marring holding of eyepieces and accessories.
2" Big Barlow in 2x Magnification
Offered in a 2x magnification, the Big Barlow is ideal for Newtonian scope owners. It will be parfocal with both 2" and 1.25" eyepieces in this application. Features include 1.25" eyepiece adapter, threads for 48mm filters, captive lock screw, and full multi-coatings. Weight = 0.75 lbs.
Note: The Big Barlow is not recommended for use with 2" diagonals because its 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 Tele Vue 2" 2x Powermate (PMT-2200), which essentially includes the Pan-Barlow Interface.
"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.