Tele Vue 2.5x 1.25" Powermate Barlow Lens - High Power Telescope Eyepiece for Astronomy & Astrophotography - Perfect for Lunar, Planetary & Deep Sky Observation

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.