"Tele Vue Barlows: ""An Optically Perfect Window "" <*> Properly designed Barlows do wonderful things. First, they amplify power while retaining the eyepiece's eye-relief. Second, they slow the telescope's f/#, which improves eyepiece sharpness. Third, the designer can introduce compensations for eyepiece aberrations. The 4x Powermate Barlow is a 4-element parfocal, compact amplifying lens system. POWERMATE consists of a negative achromatic doublet plus a positive ""pupil-correcting"" doublet. While it looks and functions like a Barlow, your eyepiece will operate with pupil locations where the designer intended, avoiding mismatch problems. POEWRMATE optimally mates its power to your eyepieces. No additional ""interface lens"" is needed, since POWERMATES have it built-in. In addition to full multi-coating, POWERMATE includes other Tele Vue special touches such as a safety undercut on the chrome barrell, and captive lock screws that can't fall out. Tele Vue's 100% QC program at f/4 insures that POWERMATE will add dramatic power (and NOTHING ELSE) to your favorite eyepieces. If, for example, you own a 22mm Panoptic, you'll have the power of a 5.5mm with the 4x POWERMATE! The 2"" 4x POWERMATE is threaded for 48mm filters. Dobsonian/Newtonian owners using Tele Vue's Paracorr coma corrector should place the 2.5x or 5x POWERMATE (or Tele Vue 2x or 3x 1-1/4"" Barlows) into the Paracorr's 1-1/4"" adapter (i.e., between the Paracorr and|Vignetting, edge field aberrations and pupil movement - all introduced when using Barlows with long focal length eyepieces, are minimized.|Telecentric operation (field rays leave parallel to optical axis, unlike Barlow lenses which diverge rays). This is ideal for Hydrogen-alpha filter use such as with Daystar models.|High performance for image amplification, CCD or film (some of the finest Earth-based planetary imaging is being done with Powermates).|Flexible for visual and imaging with all types of telescopes and eyepieces. Essentially Parfocal, and with nearly constant magnification regardless of image distance behind top surface (except 5x model which increases 1x for every 35mm of image dista|Higher magnifications are possible with high optical performance compared to ""doubling up"" Barlows.|All will reach parfocal point in star diagonals, except for the 2"", 2x which comes very close."