This 2" Astro-Tech quartz star diagonal has state-of-the-art 46-layer dielectric mirror coatings with a full 99% reflectivity for the brightest possible images. This is substantially higher than the 88% reflectivity of a conventional aluminum diagonal or the 96-97% reflectivity of an easily-tarnished silver diagonal. The Astro-Tech diagonal's quartz mirror is guaranteed to have a surface accuracy of 1/10th wave or better after the dielectric coatings are applied. Astronomy Technologies includes an interferogram of each diagonal's mirror as proof of 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.
The durable ion-deposited dielectric coatings are applied to a 10mm thick quartz substrate that 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 Astro-Tech mirror housing is precision-machined from solid aluminum, rather than simply a flimsy plastic casting or sheet metal stamping, as you'll find with ordinary diagonals. A rigid U-shaped die-cast metal backplate with stainless steel hardware holds the mirror in perfect optical alignment in the machined body. The solidity of the construction is mirrored in 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 using a metal thumbscrew that contacts eyepiece barrels directly and can scratch them, the diagonal's 2" eyepiece holder uses a non-marring soft brass compression ring to secure 2" eyepieces and the standard equipment 1.25" eyepiece adapter in place. 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 engages with 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 Astro-Tech quartz diagonal is, quite simply, unique among premium-quality 2" star diagonals for its guaranteed high performance and exceptional value. It is a visible improvement over the standard diagonal provided with virtually every refractor capable of using 2" optics. It can also be used with a Schmidt-Cassegrain or Maksutov-Cassegrain with a suitable adapter, such as the #7785C. It is an absolutely premium 2" star diagonal with guaranteed performance at a fraction the price of competitive models. The same or better performance, guaranteed, for as little as half the price. If there ever was a bargain in astronomy, this is it.
