| This 2" Astro-Tech quartz star diagonal for catadioptric telescopes 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 peak to valley or better after the dielectric coatings are applied, not before being coated, as is common with other diagonals. Astronomy Technologies includes a Zygo interferogram of each diagonal’s mirror as proof of its surface accuracy. This guaranteed 1/10th 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 diagonal has a physically short nosepiece and SCT rear cell attachment ring so it can clear the drive base on your telescope. You don’t have to buy a special version of the diagonal or special adapters to be sure that it can swing through your 8" scope’s fork arms, as you do with some competitive diagonals. The SCT rear cell attachment ring will thread directly onto Celestron SCT rear cells and onto the rear cells of those Meade SCTs that do not have an electric microfocuser as standard equipment, These Meades include older 2080 and 2120 scopes; all LX3, LX5, LX6, and Premier scopes; all current and past LX90s; and all earlier LX200 scopes that were supplied without microfocuser. The diagonal will thread onto a Meade microfocuser-equipped scope if you install the SCT rear cell adapter ring that came with the focuser into the microfocuser’s 2" drawtube. If you want a diagonal that will slip directly into the microfocuser’s 2" drawtube without needing an adapter, order diagonal #AT2DQ instead. The interior of the body is lined with light absorbing materials, in addition to being anodized an antireflective matte black. The short scope-side nosepiece that holds the rear cell attachment ring is also internally anodized matte black and is antireflection threaded for higher contrast. The attachment ring fits both Celestron and Meade rear cells. It is knurled for a sure grip so it can be easily loosened, allowing you to rotate the diagonal to the most comfortable observing position. 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 SCT diagonal is, quite simply, unique among premium-quality 2" star diagonals for its guaranteed high performance and exceptional value. The Astro-Tech quartz diagonal is a visible improvement over the standard 1.25" prism diagonal provided with virtually every Schmidt-Cassegrain or Maksutov-Cassegrain telescope. 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 premium optics, this is it.
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