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 and multi coated optics to increase light transmission and contrast with fittings for both 125 and 2 focusers it can be used with almost any telescope simply remove the rubber eyeguard to expose the t threads and attach your dslr or ccd camera with a compatible t ring the the celestron ultima duo 17mm eyepiece has 8 lens elem