1.25" 99% Reflectivity dielectric mirror diagonal

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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.

Weight:
The weight of this product.
5.5 oz.
Warranty:
2 years
Reviews from Cloudy Nights (www.cloudynights.com)
These reviews have been written by astronomers just like you and posted on the Cloudy Nights astronomy forums . . .
Asronomy Technologies 1.25 " Dielectric Diagonal model #AT1D

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Overall Product Rating: AstronomicsAstronomicsAstronomicsAstronomicsAstronomics(5.00)   # of Ratings: 4   (Only registered customers can rate)

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1. Alan on 5/17/2013, said: AstronomicsAstronomicsAstronomicsAstronomicsAstronomics
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!
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2. Paul on 5/16/2013, said: AstronomicsAstronomicsAstronomicsAstronomicsAstronomics
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.
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3. Marcy on 5/15/2013, said: AstronomicsAstronomicsAstronomicsAstronomicsAstronomics
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.
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4. jeff on 4/8/2013, said: AstronomicsAstronomicsAstronomicsAstronomicsAstronomics
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.
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Astro-Tech - 1.25" 99% Reflectivity dielectric mirror diagonal

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Astro-Tech - 1.25" 99% Reflectivity dielectric mirror diagonal
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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 . . .





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