As I'd had difficulty getting my 25mm,the worlds smallest dedicated astronomical telescope, to focus using a star diagonal (it's fine without a diagonal). I firstly tried a cheap 3x long Barlow and it focused but the length of it made the telescope unbalanced on a light tripod. I've just acquired a x2 high quality stubby Barlow and it too works id guess using a 17mm possil I'm getting around 20x magnification? I haven't tried it on the sky yet just roofs in the distance.here's the strange thing, if you put the Barlow in first,then the diagonal they eyepiece it focuses but put the diagonal in the scope, Barlow in the diagonal and eyepiece in the Barlow you can't bring it to focus....wierd!same light path but perhaps it has something to do with the focal length?