With a built-in T-adapter for astroimaging, the Ultima Duo eyepiece from Celestron is more than just an eyepiece. With fittings for both 1.25 & 2 focusers, it can be used with almost any telescope, & has 8 lens elements in 5 groups to ensure that chromatic aberration & field curvature are corrected, guaranteeing a sharp, high-quality result. Its multi-coated optics are designed to increase light transmission & contrast, & it has a 68-degree apparent field of view. Enjoy impressive views & a brilliant optical system with the Celestron Ultima Duo 21mm Eyepiece.