The Celestron CrossAim 12.5mm Illuminated Reticle Eyepiece is the perfect tool for accurate polar alignment of your telescope or for off-axis guiders during long-exposure astrophotography. The eyepiece is outfitted with a 1.25" barrel, with a 12.5mm focal length which produces a moderate magnification on most telescopes. A respectable 40° viewing angle and anti-reflection fully coated optics produce images that are bright and clear, with expansive views. A red double crosshair aiming reticle has an open center aiming square that won't obstruct small or faint objects, and is ideal for accurate initial polar alignment of the mount or to keep guide-stars perfectly centered during imaging sessions. Its LED illuminator runs on three included 1.5V alkaline button batteries, and is easy to use with a single control knob that turns it on and off with a rheostat that controls the reticle brightness to protect night-adjusted vision.