A relatively new type telescopic sight, the prismatic telescopic sight or prism scope, does away with the image erecting lens system of a traditional telescopic sight by replacing it with a prism image erector (similar to what is found in binoculars and spotting scopes). The reticle for this type of sight is etched onto one of the prism's reflection surfaces. This allows an easy way to illuminate the reticle (from the back side of the prism) and presents the viewer with a reticle even when the illumination is turned off. Since its an optical telescope, prism scopes can compensate for a user's astigmatism and, when used as a 1x sight configuration, are an alternative to reflector sights. One example of a well known series of prismatic sights is the Trijicon ACOG.