Its quartz mirror has a guaranteed surface accuracy of 1/10th wave or better, even after the dielectric coatings are applied. We include an interferogram with each diagonal to show the surface accuracy of its mirror. This guaranteed tenth-wave surface accuracy provides higher image contrast and resolution during critical planetary, lunar, and binary star observations. While designed primarily for refractors, the diagonal can also be used with a Schmidt-Cassegrain or Maksutov-Cassegrain telescope by adding a suitable optional rear cell adapter.

The diagonal’s stable 10mm thick quartz mirror substrate has better thermal expansion and contraction characteristics than a conventional glass mirror. There’s no need to worry about the focus changing as the diagonal cools down to ambient temperatures.

The mirror housing is precision-machined from solid aluminum, rather than flimsy molded plastic or a sheet metal stamping, as you find with ordinary diagonals. A rigid U-shaped die-cast aluminum backplate with stainless steel hardware holds the mirror in perfect optical alignment in the machined body. The solid construction is demonstrated by the diagonal’s substantial 17 ounce weight.

The interior of the body is lined with light absorbing materials, in addition to being anodized an antireflective matte black. The 2” focuser-side barrel is also anodized antireflective matte black, and is internally antireflection threaded for even higher contrast. The barrel is threaded to accept standard 2” filters.

Rather than holding eyepieces in place with a metal thumbscrew that contacts eyepiece barrels directly and can scratch them, the 2” eyepiece holder uses a non-marring soft brass compression ring to secure eyepieces and the standard equipment 1.25” eyepiece adapter. The knurled and chromed thumbscrew that operates the compression ring is a full 1/2” in diameter, twice that of many competitive diagonals. This provides a sure grip in cold weather when wearing gloves or mittens. A slanted groove cut into the outside of the focuser-side 2” barrel catches the scope’s focuser drawtube thumbscrew to act as a safety stop. This keeps the diagonal from falling should the scope’s thumbscrew loosen slightly from cold or use.

The supplied 1.25” eyepiece adapter also uses a compression ring to hold eyepieces in place. The scope-side barrel of the 1.25” adapter is likewise grooved to keep it from accidentally slipping out of the 2” diagonal. Dust covers are provided for the 1.25” adapter and the diagonal’s 2” barrel.

With all these advanced features, this quartz diagonal is, quite simply, unique among premium-quality 2” star diagonals. It provides guaranteed and documented performance at a fraction the price of competitive models. If there ever was a bargain in astronomy, this is it.