This 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 – and it’s still a hot product for many observers.
The Astro-Tech 1.25” diagonal has state-of-the-art 46-layer dielectric mirror coatings for a full 99% reflectivity. This is markedly higher reflectivity 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, changing your viewing from “I guess I see it” to “it’s really there!”
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, rather than simply flimsy Bakelite plastic or a sheet metal stamping, as you’ll find with ordinary diagonals. A rigid machined metal backplate with stainless steel hardware holds the mirror in perfect optical alignment in the machined body. The interior of the body is anodized an antireflective matte black. The 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 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.
This premium 1.25” diagonal works with virtually any Schmidt-Cassegrain, Maksutov-Cassegrain, or refractor that uses a 1.25” star diagonal,. It will provide a visible improvement over the scope’s factory-supplied diagonal. The newly designed body of the Astro-Tech diagonal is more compact than previous diagonals. This essentially eliminates any possibility of the diagonal bumping into the drive base of a short fork arm catadioptric when the scope is pointed at the zenith. This Sky & Tel Hot Product gives you all the visual performance your scope is capable of delivering, at a price that’s very affordable.