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 Para