Televue Powermate lenses are at the top of their class. Thanks to their impeccable optics, they are the best choice for those who want to achieve the best quality focus extension in planetary photography. Their design is also outstanding: the focuser is fitted with a clamping ring that does not "push" the eyepiece out of the optical axis or scratch the eyepiece when it is mounted.
Powermates differ from "ordinary" barlow lenses in their construction. They do not produce vignetting, which is particularly beneficial when used with SLR cameras.