Celestron Telescope Binocular Stereo Viewer. In addition to eliminating eye fatigue associated with viewing through one eye for a prolonged period of time this bino viewer also provides a three dimensional effect while observing many celestial objects. The Stereo Binocular Viewer 93691 will also improve contrast on deep sky objects as well as solar system objects. The Celestron Stereo Binocular Viewer is designed to work with Schmidt-Cassegrain telescopes (SCT) and many refracting telescopes. Features high quality FMC BAK-4 prisms reduce light loss. Each unit is quality control inspected for collimation and performance. The Celestron 93691 Stereo Bino Viewer requires you use two eyepieces of equal focal lengths and optical design. Specifications for Celestron Binocular Stereo Viewer 93691: APERTURE: 18 mm (0.71 in) PRISMS: BaK-4 OPTICAL COATINGS: Fully Multicoated with Broadband Coatings WEIGHT: 18.4 oz (521.63 g) Features of Celestron Bino Viewer 93691: Fully Multi-Coated BAK-4 prisms Foam lined aluminum storage case Eyepiece diopter scales for sharp focus Package Contents: Celestron Telescope Binocular Stereo Viewer 93691