Star Diagonals

A star diagonal redirects the light path in refractors, Maksutov-Cassegrain and other telescopes so you can observe at a comfortable angle, especially when viewing objects high overhead. Explore Scientific dielectric star diagonals use highly reflective coatings to deliver bright, high-contrast images, and are available in 1.25-inch, 2-inch and 3-inch sizes to suit telescopes and eyepieces of all sizes.

A quality diagonal is one of the most important, and most overlooked, parts of an optical system, because every photon passes through it on the way to your eye. Upgrading to a high-reflectivity dielectric diagonal can noticeably improve brightness and contrast on faint deep-sky objects. This collection also includes BinoViewers, which split the light so you can observe with both eyes for a more relaxed, immersive view of the Moon and planets.

When choosing a star diagonal, match the size to your focuser and eyepieces: 1.25-inch diagonals suit smaller telescopes, 2-inch diagonals accept wide-field eyepieces and usually include a 1.25-inch adapter, and 3-inch diagonals support large-format eyepieces on big telescopes. A secure compression ring or twist-lock holds eyepieces safely. Star diagonals are used with refractors, Maksutov-Cassegrain and Schmidt-Cassegrain telescopes, but are not needed with Newtonian reflectors or Dobsonians, which already provide a side-mounted eyepiece position.