Astro-Tech 1.25" 99% reflectivity dielectric quartz mirror diagonal

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In addition to 99% reflectivity dielectric coatings, this Astro-Tech 1.25" star diagonal has a premium first-surface mirror made of low thermal expansion quartz, rather than conventional BK7 glass . . .

Our Product #: AT1DQ
Astro-Tech Product #: AT1DQ

Product Description


This 1.25" Astro-Tech star diagonal is quartz mirror upgrade to the original (and still available) Astro-Tech diagonal named a Sky & Telescope Hot Product for 2007. Like the original, the AT1DQ uses high transmission/high contrast dielectric mirror coatings, but substitutes a low thermal expansion quartz mirror for the original's BK7 optical glass mirror. This premium-quality diagonal brings all the optical benefits of a 2" quartz diagona to scopes that can only use 1.25" accessories.

The Astro-Tech AT1DQ 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 quartz substrate have an exceptionally smooth surface. Since less light is scattered by the smooth 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 quartz mirror substrate has low thermal expansion characteristics, so you don't have to worry about focus change issues as your diagonal and scope acclimate to the nighttime temperature.

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 Astro-Tech quartz mirror diagonal gives you all the visual performance your scope is capable of delivering, at a price that's very affordable.

Tech Details

Weight 5.5 oz.
Warranty 2 years


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