Orion 8754 1.25-Inch Deluxe 45-degree Correct-Image Prism Diagonal Turn any refractor or Cassegrain telescope into a high-performance daytime spotting scope with our Deluxe 45 Degree Correct-Image Diagonal High-quality prism diagonal provides a comfortable, 45 Degree viewing orientation for great daytime terrestrial views Sporting a 27mm clear aperture, multi-coated prism, Deluxe 45 Degree Correct-Image Diagonal provides sharp views 3 arc second tolerance prism is 35% larger than prisms used in other models