Sky watcher explorer 250pds 254mm 10 f1200 parabolic dual speed newtonian reflector optical tube assembly the new sky watcher explorer 250pds newtonian reflector incorporates the same superb mirror set as the explorer 250p black diamond series but with two significant advantages a dual speed 101 ratio focuser is now included for excellent focusing precision also the tube length has been slightly shortened to optimise performance for prime focus photographyeven better performance for as