HUD HS510C Circle Dot Sight with open frame and integrated dual laser sights Sight stays always powered . on. It is powered by solar cell under normal usage but under low light conditions the battery will supplement the power requirements. As required the reticle can be switched between circle and red Dot. - Features - When focussing on the target the size of circle reticle will change based on the distance between your eyes and eyepiece lens. - Parallax free optical design witunlimited eye relief. - Minimized obstruction of vision with push button controls and streamlined housing design. - Switchable circle and red dot reticles. - Always on power under all light condition. - Battery tray design. - 32mm