Astro-Tech 2" 99% Reflectivity Dielectric Mirror Secure-Lock Diagonal For Refractors


Availability: In stock

This 2” dielectric mirror-type Secure-Lock star diagonal is an outstanding value. At this low price, if there ever was a bargain in astronomy, this is it . . .

Our Product #: AT2D

Product Description

This 2” Astro-Tech Secure-Lock first-surface mirror star diagonal 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.

The 2" eyepiece/accessory holder introduces a new Secure-Lock mechanism. Rather than using a single metal thumbscrew or metal compression ring to hold eyepieces in place, the 2” Secure-Lock eyepiece holder has a large ribbed ring at the top that secures 2” eyepieces and accessories. Less than quarter turn of the ribbed ring locks polymer ribs inside the adapter's 2" barrel evenly and firmly around the 2" eyepiece or accessory. This secures the eyepiece or accessory in place and centers it in the 2" accessory holder. The large ribbed ring provides a sure grip in cold weather when wearing gloves or mittens. A separate knurled and chromed thumbscrew can lock the ribbed ring in place as an extra safety measure.

The supplied 1.25” eyepiece adapter uses a compression ring to hold eyepieces in place. The scope-side barrel of the 1.25” adapter has a subtle slanted groove to keep it from accidentally slipping out of the 2” diagonal. Dust covers are provided for the 1.25” adapter and the diagonal’s 2” barrel.

The interior of the diagonal body and the inside of the focuser-side barrel are treated with light absorbing materials. The focuser-side barrel is also internally anti-reflection threaded for even higher contrast. The barrel is threaded to accept standard 2” filters.

A subtle slanted groove cut into the outside of the focuser-side 2” barrel engages with your telescope’s focuser thumbscrew to act as a safety stop. This keeps the diagonal from falling should the scope’s thumbscrew loosen slightly from cold or use.

This diagonal is a visible improvement over the conventional 2" diagonal provided with many refractors capable of using 2” optics. It can also be used with a Schmidt-Cassegrain or Maksutov-Cassegrain telescope with a suitable adapter, such as the #7785C. It is an absolutely premium 2” 99% reflectivity dielectric self-centering star diagonal at a fraction the price of competitive models with equivalent performance and build quality. The same performance, for as little as half the price. If there ever was a bargain in astronomy, this is it.

Tech Details

Weight 17 oz.
Warranty 1 year


Review by:
Bright and clear views with this diagonal. I also own the 1.25" and both perform wonderfully! (Posted on 10/7/2018)
Review by:
I've owned this diagonal for 10 years and it's one great diagonal. I can find no significant flaws in it. It's well designed, very well built and has never given any trouble. The coatings are as good as brand new and after several AB comparisons, the performance is comparable to the 2" TV Everbrite, which I sold to fund other accessories after getting the AT. The clear aperture is large enough to match my 31T5 with no vignetting at all. I highly recommend this product. (Posted on 10/6/2018)
Review by:
The build quality of the Astro-Tech 2" Diagonal was apparent the moment it was in hand. The fit and finish are first rate. Its optical performance is superb. I have owned more expensive 2" diagonals but none have presented better views. (Posted on 10/6/2018)
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