The 2" Erecting Prism Diagonal from Olivon is a telescope accessory useful for both stargazing and land observation. An erecting prism diagonal correctly orients the telescope's transmitted image so that the eyepiece can be viewed without unnecessary neck strain. This feature is especially helpful when viewing subjects at the horizon or high in the sky. The diagonal's erecting prism is made of BaK4 optical glass and is fully multicoated for maximum light transmission. Thanks to an included adapter ring, this diagonal can be used with either a 1.25" or 2" focus tube.