The Astro Tech 1.25" Dielectric Mirror star diagonal is unique among 1.25" star diagonals for its amazing value. The Astro Tech 1.25" Dielectric Diagonal has a 46 layer dielectric mirror coatings for 99% reflectivity. The Astro Tech AT1D 1.25" Dielectric Mirror Diagonal is our most popular diagonal because of the value it offers to the consumer. The Astro Tech 1.25" Dielectric Diagonal has an amazing finish, weighs 5.5 ounces and comes with a full two year warranty.
Below is a full description of the Astro Tech AT1D 1.25" Dielectric Diagonal from Astronomy Technologies.
This diagonal has state-of-the-art 46-layer dielectric mirror coatings for a full 99% reflectivity. In addition to higher reflectivity than the 88% of a conventional aluminum diagonal or the 97% of an easily-tarnished silver diagonal, the durable ion-deposited dielectric coatings on the mirror's finely-polished BK7 optical glass substrate also provide higher contrast and resolution during critical planetary, lunar, and binary star observations.
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 die-cast metal U-shaped 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 7 ounce weight. The interior of the body is lined with light absorbing materials, in addition to being 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 secure eyepieces in place, rather than a thumbscrew that contacts the eyepiece barrel directly and can scratch it. 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 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 is an absolutely premium 1.25" diagonal at an absolutely sensational price. It will give you all the visual performance your scope is capable of delivering, at a very affordable price. It's a worthy and visible upgrade for virtually any Schmidt-Cassegrain, Maksutov-Cassegrain, or refractor that uses a 1.25" star diagonal.
