"Allows you to use 1.25"" eyepieces on Questar scopes.Unleash the potential of your Questar. Just add this adapter to use any of the Tele Vue 1 1/4"" eyepieces: Plossls, Radians, Panoptics, and Naglers!Experience a greater range of magnification, quick-change capability, and parfocalization (no need to adjust focus when changing eye pieces).Discover improved resolution, color correction and contrast due to the multicoating, blackened lens edges, and new designs.The threaded eyepiece barrels accept Nebular and other filters, if desired.And, with fields of view up to 82 degrees, diffraction limited anywhere in the field, your Questar 3 1/2 finally delivers the magnificent capability inherent in its design and construction. Overall, we recommend the Nagler 9mm and Panoptic 19mm.This finely crafted piece is CNC machined out of solid aluminum stock to complement the Questar. Its polished aluminum base has blackened anti-reflection threads on the inside aperture to improve contrast. A black anodized knurled focusing ring allows focusing to the Questar viewfinder optics, and a lock screw (with 2 locations for convenience) gives extra security."