The Explore Scientific focus extenders are special barlow lenses: first of all, they extend the focus of the telescope, but in a different way than barlow lenses: thanks to its complex lens exchange system, the image is not vignetted even with long-focus eyepieces, and the pupil distance of the eyepieces is maintained.
Excellent image sharpness and image contrast, as expected from Explore Scientific products, and a self-contained constriction ring design.