This thing it great! it's just a little dimmer that my 55mW pen but it beats it on beam spec's as it's 0.9mRad! as it focusable. To focus it you need to unscrew the head and turn the lens with your hand. It uses a CR123A battery and i have not needed to change the battery in days, so it has a great run time. So glad i bought it.. was going to use it has a host but i can't bring myself to open as i don't won't to risk breaking it. Heres a beam pic!