Combining a brilliant optical system with a built-in T-adapter for astroimaging, the Ultima Duo eyepiece from Celestron has a wide 68-degree apparent field of view, & multi-coated optics to increase light transmission & contrast. With fittings for both 1.25 & 2 focusers, it can be used with almost any telescope: simply remove the rubber eyeguard to expose the T-threads, & attach your DSLR or CCD camera with a compatible T-ring. The The Celestron Ultima Duo 17mm Eyepiece has 8 lens elements in 5 groups to ensure that chromatic aberration & field curvature are corrected, guaranteeing a sharp, high-quality result.