The 2 Inch Diagonal Telescope allows you to take advantage of the wider field of view provided by 2 inch telescope eyepiece; enjoy better views through your telescope with this premium diagonal featuring diffraction-limited optics and dielectric coatings Premium Image: The 2 inch SCT diagonal features dielectric coatings with 93% percent reflectivity across the visible spectrum and a 1/10 wave mirror for bright and true images and extends the life of the surface Wide Applicability: It fits all rear cells of Schmidt Cassegrain telescopes and includes an adapter to use with refractor telescopes; with standard SCT female thread attach directly to Schmidt Cassegrain telescopes and many Maksutov Cassegrain telescopes 90 Degrees Design: Associated with 90 degree mirror diagonals which let you view objects that are at a 90 degree angle from the direction the telescope is pointing; which can provide you with a better observation experience during visual observation Superior Aluminum Materials: It is constructed from aluminum alloy; which significantly enhances the 2 Inch star diagonal longevity; improved attachment design features a brass clamping ring which does not mar and provides a more secure connection Astromania's 2" SCT mirror diagonal is an excellent alternative to higher priced diagonals for those on a budget or just getting started in the 2" format. The 2" SCT diagonal features dielectric coatings with 93% reflectivity across the visible spectrum and a 1/10 wave mirror. The all metal diagonal body is CNC machined. The combined result is a superb diagonal offering excellent mechanical and optical quality at a great value. You can attach this diagonal directly to Schmidt-Cassegrain telescopes and many Maksutov-Cassegrain telescopes, as long as there is a SCT male thread on the telescope. The standard SCT thread is a 2"x24tpi thread.Star diagonal is the term commonly associated with 90°mirror diagonals such as this, which let you view objects that are at a 90°angle from the direction the telescope is pointing. This allows quite comfortable viewing when the telescope is at or near the zenith. Upgrading your diagonal and switching to 2" eyepieces is one of the best investments you can make in your telescope. The wider diagonal captures more of the telescope's light cone, perfect for viewing faint, deep sky objects like nebulae and galaxies.