The 1.25” Astro-Tech first-surface mirror star diagonal was named a Sky & Telescope Hot Product for 2007! Sky & Tel recognized that the Astro-Tech diagonal would be an outstanding value at even twice its low price. As it is, this Astro-Tech diagonal is unique among 1.25” star diagonals for its exceptional price/performance ratio. This is one premium-quality diagonal that doesn’t happen to be priced like one.
The Astro-Tech 1.25” diagonal has state-of-the-art 46-layer dielectric mirror coatings for a full 99% reflectivity, markedly higher than the 88% of a conventional aluminum diagonal or the 96-97% of an easily-tarnished silver diagonal. The result? Extremely faint objects at your scope’s performance limits become more visible, and the contrast range is improved on all objects.
In addition, the durable ion-deposited dielectric coatings on the mirror’s finely-polished 1/10th wave BK7 optical glass substrate have an exceptionally smooth surface. Since less light is scattered by the dielectric surface than by the minor 1/20th wave to 1/200th wave surface irregularities of an aluminized mirror, you see subtly higher contrast and resolution with the Astro-Tech during critical planetary, lunar, and binary star observations.
The mirror housing is precision-machined from solid aluminum. The interior of the body is anodized an antireflective matte black. The focuser-side barrel is internally antireflection threaded for high contrast. The barrel is threaded to accept standard 1.25” filters.
The 1.25” eyepiece holder uses a non-marring soft brass compression ring to clamp eyepieces in place, rather than a thumbscrew that can scratch an eyepiece barrel by tightening down on it directly.
A shallow slanted groove cut into the outside of the focuser-side barrel engages with the scope’s visual back or eyepiece holder thumbscrew to act as a safety stop. This keeps the diagonal from falling should the scope’s thumbscrew loosen slightly from cold or use. Dust covers are provided for both sides of the diagonal.
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