Astro-Tech 2" 99% Reflectivity dielectric mirror diagonal for SCTs


Availability: In stock

This 2" dielectric mirror-type star diagonal is designed to give you first-class performance with a Schmidt-Cassegrain - at a money-saving and far from first-class price . . .
Our Product #: AT2SD
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Product Description

This 2" Astro-Tech first-surface mirror star diagonal for catadioptric telescopes has state-of-the-art 46-layer dielectric mirror coatings for a full 99% reflectivity, higher than the 88% of a conventional aluminum diagonal or the 96-97% of an easily-tarnished silver diagonal. The durable ion-deposited dielectric coatings on the mirror's finely-polished 10mm thick 1/10th wave BK7 optical glass substrate also provide higher contrast and resolution during critical planetary, lunar, and binary star observations. It has a physically short nosepiece and SCT rear cell attachment ring so it can clear the drive base on your telescope. You don't have to buy a special version of the diagonal or special adapters to be sure that it can swing through your 8" scope's fork arms, as you do with some competitive diagonals. This Astro-Tech diagonal is, quite simply, unique among premium-quality 2" SCT star diagonals for its exceptional value.

The SCT rear cell attachment ring will thread directly onto Celestron SCT rear cells and onto the rear cells of those Meade SCTs that do not have the electric microfocuser as standard equipment, These include older 2080 and 2120 scopes; all LX3, LX5, LX6, and Premier scopes; all current and past LX90s; and all earlier LX200 scopes that were supplied without microfocuser. The diagonal will thread onto a microfocuser-equipped scope if you install the SCT rear cell ring that came with the focuser into the microfocuser's 2" drawtube. If you want a diagonal that will slip directly into the microfocuser's 2" drawtube, order diagonal #AT2D 2" 99% Reflectivity dielectric mirror diagonal for refractors instead.

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 short nosepiece that holds the rear cell attachment ring is internally antireflection threaded for high contrast. The attachment ring fits both Celestron and Meade rear cells. It is knurled for a sure grip so it can be easily loosened, allowing you to rotate the diagonal to the most comfortable observing position.

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 firmly hold 2" eyepieces and the standard equipment 1.25" eyepiece adapter. The knurled chrome 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.

The 1.25" eyepiece adapter also uses a compression ring to hold eyepieces in place. The 1.25" adapter has a slanted groove cut into the outside of its focuser-side 2" barrel. This engages with the diagonal's compression ring to act as a safety stop to keep the adapter from accidentally slipping out of the 2" diagonal should the compression ring loosen during use. Dust covers are provided for the 1.25" adapter and the diagonal's SCT attachment ring.

This diagonal is a visible improvement over the standard 1.25" prism diagonal provided with virtually every Schmidt-Cassegrain or Maksutov-Cassegrain telescope. It is an absolutely top-rank 2" 99% reflectivity dielectric star diagonal at only a fraction the price of competitive models with equivalent performance and build quality. The same premium performance, for as little as half the price. If there ever was a bargain in SCT astronomy, this is it.

Tech Details

Weight 17 oz.
Warranty 1 year


Review by:
I’m new to amateur astronomy,mind bought a gently used Celestron 9.25 SCT. The weak link always seemed to be the original diagonal attachment using screws. By having the direct mount to the OTA, the fiddliness of the set screw mounting is eliminated, and I am much less concerned about dropping something expensive in the dark. (Posted on 10/4/2019)
Review by:
I have owned this great diagonal for over a year now and it performs as well as my Celestron diagonal. It has a great finish. I especially like how easy it is to attach to the SCT or CPC. Very happy and pleased with this product. A++++ (Posted on 9/10/2019)
Review by:
This Astro-Tech diagonal replaced the weakest link on my vintage 1993 Meade 12" LX200. Combined with a selection of Televue eyepieces it has allowed me to get the most out of a well cared for classic scope. (Posted on 8/2/2019)
Review by:
This Astro-Tech 2" diagonal replaced the weakest link on my vintage 1993 Meade 12" LX200. Combined with a selection of Televue eyepieces it's allowed me to get the most out of a well cared for scope. (Posted on 8/2/2019)
Review by:
Decent build quality for the price, has a nice hefty feel. Love the compression ring that keeps your eyepieces pristine. Probably the best diagonal in this price range. (Posted on 1/14/2019)
Review by:
I have a Televue Everbrite star diagonal, and this AstroTech compares favorably with it at a fraction of the price. The build quality is excellent throughout. Works perfectly with all my 2” EPs as well as with my 1.25 EPs using the included adapter. Highly recommended. (Posted on 1/12/2019)
Review by:
This has to be one of the best values out there for a 2" dielectric diagonal. The build quality reminds me of Televue but at a fraction of the cost. The difference between my 1-1/4" stock diagonal and this one is startling. The brass compression ring ensures that eyepieces will not be marred when the thumb screw is tightened. I'll get the non-SCT version of this when I get an APO. (Posted on 10/6/2018)
Review by:
This diagonal is clearly a step up from the stock 1-1/4" that came with the telescope; the difference is startling. Flawless, Televue-like quality but at much less the cost. Would buy another Astro Tech diagonal for a non-SCT application for my future APO. (Posted on 10/6/2018)
Review by:
I bought this for my 8" SCT when I bought meh first 2" eyepieces. I love the way it connects so securely to my OTA with no tools or screws. The quality is great, and the optics are fantastic with my new Nagler eyepiece. (Posted on 10/6/2018)
Review by:
I have had this diagonal for a few years. It is by far the best diagonal I have owned. Very well made. Impressive!! (Posted on 10/6/2018)
Review by:
Awesome diagonal,very clear mirror and very attractive finish and at one pound it's not overly heavy.Threads securly to rear cell of SCT,Great for binoviewers. (Posted on 8/4/2017)
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