Astro-Tech 1.25" 99% Reflectivity dielectric mirror diagonal


Availability: In stock

This 1.25" dielectric mirror-type star diagonal was a Sky & Telescope Hot Product for 2007! Considering its performance, it would be an outstanding value at twice the price. At its economical low price, it's still a hot product, and nothing short of sensational . . .
Our Product #: AT1D

Product Description

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 deep space objects at your scope's performance limits become more visible, changing your viewing from "I guess I see it" to "it's really there!"

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 on deep space objects 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.

Tech Details

Weight 5.5 oz.
Warranty 1 year


Review by:
I have purchased two of these diagonals over the years: one to use with my Tele Vue TV60 and one for a 90mm Maksutov. The quality of the build is very solid, and it delivers bright clear views through both scopes. At the price, these Astro Tech diagonals are one of the best bargains around in amateur astronomy. Definitely recommended. (Posted on 7/22/2019)
Review by:
This diagonal has been fantastic since I've been using it with the AT65EDQ. It gives great views from center to edge and matches well with all of my Plossls as well as my Mead UWA eyepieces. (Posted on 1/7/2019)
Review by:
I use the 1.25" diagonal exclusively on my 80 mm refractor. At this price, it's easy to have a dedicated diagonal for each of my main refractors. (Posted on 1/3/2019)
Review by:
This diagonal would be a great deal at 99.00. At 69.00 it is a steal. I use it with my 72 and it is terrific. Did I mention its only 69.00 for dielectric reflectivity? (Posted on 11/25/2018)
Review by:
Bought this for my original AT72. Works great and provides a very clear image. Consider it my workhorse of diagonals. Not to mention the price is a great incentive on its own... (Posted on 11/24/2018)
Review by:
Must have to allow for good viewing angles without standing on your head. I have used this over the last year and it works great. Solid connection to eyepiece so when slewing you do not hear that "ding" once things rotate in the wrong direction in the dark as your expensive eyepiece falls to the concrete........ (Posted on 11/3/2018)
Review by:
I purchased this nearly two years ago as an upgrade from the diagonal included with my Meade Infinity 102. It works great with my Astro-Tech Paradigms. It's good to have a diagonal that matches the quality of the eyepieces. The machining, fit, and finish are first rate. Highly recommended. (Posted on 10/24/2018)
Review by:
I use this diagonal and the 2" diagonal. Both perform wonderfully! (Posted on 10/7/2018)
Review by:
I use this diagonal with my 70 mm refractor when I am using 1.25 inch eyepieces. It is a very high quality diagonal that is priced very fairly. Another excellent product from Astro-Tech! (Posted on 10/6/2018)
Review by:
I have collected accessories I can rely on, and this diagonal is one of them. If I see an image aberration through this diagonal, I will check the eyepiece or the scope first. (Posted on 10/6/2018)
Review by:
Dielectric mirror for $69 bucks? That's a good deal. Astro Tech has produced a great product in this 1.25" star diagonal. Build quality is excellent throughout. Compression ring fits and holds eyepieces securely without marking. Nosepiece fits properly into scope without slop. Viewing is first rate across the field, as one would expect. Nicely boxed with quality end caps. Exactly what I was looking for! (Posted on 8/4/2017)
Review by:
Several years ago I purchased a 6" Celestron refractor. With the length of the tube a diagonal is somewhat of a necessity unless you want to lay on the ground and look through the eyepiece! One of the issues with a diagonal is their spotty quality. You can tell a big difference between a straight through view and one through a diagonal. Usually the non-diagonal view is much better and brighter. In fact both of my 1.25" diagonals from major manufacturers had distorted and dim views. Not so with the Astrotech 1.25" diagonal! Other than the right side up and backwards orientation with the dielectric diagonal in place there was no discernible drop in quality. I have been using this diagonal for around 4 years and have found it to be well made, well fitted and durable. I purchased the 1.25" unit due to the fact that I have no 2" eyepieces and at the time of purchase was going to spend most of the observing time imaging so buying a 2" seemed superfluousness.
I have no qualms about recommending this diagonal for general 1.25" use. It is definitely worth the money and will perform at a high level for many years. (Posted on 8/4/2017)
Review by:
I have had this diagonal for several years now, and have been very happy with it. Fit and finish are impressive for such a reasonably priced piece of equipment, and although subtle I can really see a difference in the views when compared with my old diagonal. I have had friends test it out and they, too, were impressed. Would definitely recommend. (Posted on 8/4/2017)
Review by:
I've been very happy with this diagonal. It's very well made and gives clear, bright views. I use it on an ST-80. The purchasing and shipping process was fast and I would definitely recommend the diagonal and Astronomics, in general. (Posted on 8/4/2017)
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