The Tele Vue 2.5X PowerMate Image Amplifier in 1.25-inch size.A Pupil-Corrector, Extender/ Amplifier at its best!
"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. My 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, I hope you'll agree PowerMate raises the standard for image amplification."- Al Nagler
The 2.5X PowerMate is a 4-element concept which continues the tradition of full-field sharpness with optimum aberration control. Are you looking for long eye-relief? The Tele Vue PowerMate (#TE-PMT-2513) retains the eye-relief of long focal length eyepieces, while at high power... a bonus for all eyeglass wearers! What makes it special? The Tele Vue PowerMate consists of a negative doublet plus a positive "pupil-correcting" doublet. This 4-element system provides the magnifying function of a barlow without its limitations by restoring the field rays back to their original direction... as if the PowerMate wasn't there. The result is a pure magnification increase! The 2.5X is flexible for visual and imaging with all types of telescopes and eyepieces. Essentially parfocal, the Tele Vue PowerMate delivers nearly constant magnification regardless of image distance behind top surface. Vignetting, edge field aberrations and pupil movement are minimized.
For astro-imagers, check the "Gallery" tab for a chart which indicates the magnification as a function of distance from the Televue Powermate top surface to the imaging surface (CCD or film). Some of the finest Solar System images on this world have been made with Tele Vue PowerMates! Used singly or stacked, they help any scope achieve the long focal-length required to image details on the planets or solar surface. The increased image scale allows for imaging without an intervening eyepiece -- like in prime focus photography.