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This 2” Astro-Tech first-surface mirror star diagonal has enhanced aluminum mirror coatings whose reflectivity and performance are comparable to diagonals more than twice its sensible price. It is, quite simply, unique among 2” star diagonals for its exceptional price/performance ratio. This is one premium-quality star diagonal that isn’t priced like one. The diagonal uses a finely-polished 10mm thick BK7 optical glass substrate for stability in changing thermal conditions. The mirror housing is precision-machined from solid aluminum, rather than simply flimsy plastic or a 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 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 1.25” eyepiece adapter uses a compression ring to hold 1.25” eyepieces in place. The barrel of the 1.25” adapter is 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. This is an absolutely premium 2” enhanced aluminum diagonal for a price as little as half that of comparable competitive models. It’s a worthy and visible upgrade for virtually any refractor capable of using 2” optics. It can also be used with a Schmidt-Cassegrain or Maksutov-Cassegrain with a suitable 2” rear cell adapter.
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