Powermate Concept: While Barlows are powerful tools, the negative element defining them also limits their ability. The simple negative element Barlow increases eyepiece eye-relief. With short focal length eyepieces the effect is negligible. However, on long focal length eyepieces the exit pupil position moves well beyond the designer's intended position, resulting in vignetting with many eyepieces. This is why "Shorty" Barlows in particular, with their strong negative element often vignette and degrade long focus eyepieces. Al Nagler's 4-element form picks up where the Barlow concept can go no further. Powermate™ is a technically universal solution, using a positive field lens to redirect field rays. The result is an exit pupil that stays where the eyepiece designer intended. With freedom from aberrations, greater magnification potential, and compact size, Powermate™ raises the standard for image amplification.
This new model is nearly parfocal (unlike the Big Barlow / Interface combination), so it can be effectively used in TeleVue's 2" diagonals. Its performance is excellent with every 1.25" or 2" eyepiece (even the 31mm Nagler Type 5!). Both the 2" eyepiece holder and the special 2"-1.25" low-profile adapter use TeleVue's brass clamp rings for secure, non-marring operation. And it also has a very unique feature: you can unscrew the 2" eyepiece housing and screw on an optional T-ring adapter (part number PTR-2200) for solid, compact attachment of CCD or camera equipment.