A star diagonal turns the light path, usually by 90°, between the focuser and the eyepiece so you can look down comfortably into a refractor, SCT or Maksutov aimed high in the sky. Dielectric mirror diagonals such as the Explore Scientific 99% and SVBONY SV223 give high reflectivity, prism diagonals like the Baader BBHS prism and Takahashi 1.25" prism suit slower refractors, and erect-image prisms such as the Baader Amici or William Optics 45° give a correctly oriented view for daytime use; match the fitting (1.25-inch, 2-inch or SCT thread) to your telescope. To raise magnification with the same eyepieces, see Barlows & Focal Extenders.
