Brand: Celestron

Celestron Dielectric Star Diagonal 2" Twist-Lock (93573)


Brand: Celestron

Celestron Dielectric Star Diagonal 2" Twist-Lock (93573)


  • Enjoy better views through your telescope with this premium diagonal featuring diffraction-limited optics and dielectric coatings
  • Provides a 90° viewing angle, perfect for more comfortable viewing through refractor and Cassegrain-type telescopes
  • 58 layers of dielectric coatings provide an over 99% reflective surface, ensuring the maximum amount of light collected by the telescope reaches the eyepiece
  • Twist-lock keeps the eyepiece centered in the diagonal to provide better optical alignment
  • Includes a stepdown adapter, so the diagonal accepts eyepieces, Barlow lenses, threaded filters, and other accessories in both 2” and 1.25” sizes
  • Two interchangeable adapters allow you to switch between a Schmidt-Cassegrain thread adapter and a 2” barrel adapter so you can use this diagonal with a wide variety of telescopes
$249.95 USD

Easy Payment Options with .

$249.95 USD

Easy Payment Options with .

Free Expert Support
Stress Free, Secure Shopping
30 Day Return Policy
Price Match Promise
Full Details Specifications Reviews and Questions

Product Description

Ensure maximum light transmission without loss of optical quality with the Celestron Dielectric Star Diagonal, 2” with Twist-Lock. Upgrade your existing star diagonal to this premium one and enjoy brighter, sharper images without purchasing an entirely new telescope.

This star diagonal reflects the telescope’s light path 90° to provide a more comfortable viewing angle. In addition, the glass has 58 layers of dielectric coatings, which provide an over 99% reflective surface, delivering the maximum amount of light to the eyepiece. This 2” star diagonal has the added benefit of allowing you to use larger 2” eyepieces with your telescope, providing a wider field of view, or standard 1.25” eyepieces with the stepdown adapter.

The twist-lock eyepiece holder secures eyepieces while keeping them centered in the diagonal, thus providing best opto-mechanical alignment between the telescope and eyepiece. Unlike traditional thumb screws, the twist-lock cannot scratch or engrave the barrel of your eyepieces. The diagonal has an integrated 2” barrel stop that prevents 2” accessories with long barrels from damaging the mirror.

All the diagonal’s mechanical parts are made of machined black anodized aluminum, except the twist lock rings, which are orange anodized for visibility. The interior of the Schmidt-Cassegrain adapter and 2” barrel are glare threaded and painted flat black to prevent glare. With all its features and these high-end finishes, the Celestron Dielectric Star Diagonal, 2” with Twist-Lock is one of the highest quality 2" star diagonals that Celestron has ever offered.

This diagonal also comes with two interchangeable barrels to provide flexibility in connecting the diagonal to a wide variety of telescopes without the need for additional adapters. For telescopes, like refractors, which accept 2” barrels in their focuser, a standard 2” barrel is included. For Schmidt-Cassegrains (SCTs) that use a threaded connection to the focuser, a barrel with SCT threads is included. Both barrels thread onto the diagonal housing, providing a secure connection to the diagonal.

Standard Star Diagonals vs Dielectric Star Diagonal

The key specifications for a star diagonal are its reflectivity and its optical quality. This diagonal delivers top performance in both categories, with an over 99% reflective mirror and diffraction-limited optical quality. This ensures that virtually all the light collected by the telescope will reach the eyepiece without the diagonal affecting optical performance. Using a lower quality star diagonal can both dim the view and degrade optical quality. You can enjoy better views from your telescope by simply swapping out its diagonal for a premium one, like the Celestron Dielectric Star Diagonal.


Diagonal size: 50.8mm (2")
Diagonal type: Mirror
Glass material: BK7
Coatings: Dielectric, 58 layers
Reflectivity: Over 99%
Optical quality: Diffraction limited
Eyepiece holder: 2", Twist-Lock
2"-to-1.25" Stepdown adapter: Included, Twist-Lock
Compression ring: Yes, dual rings for 2" eyepiece holder and single ring for 1.25" stepdown adapter
Housing construction: Machined aluminum black anodized
Barrels: Comes with 2" barrel (for connection to 2" focusers) and SCT adapter (for connection to SCTs)
Barrel interior: Glare threaded and painted flat black
Threads for filters: 2" barrel and 1.25" stepdown adapter have 2" filter threads
Dimensions: 152.4mm x 76.2mm x 101.6mm (6" x 3" x 4")
Weight: 19 oz (538.6 g) (with stepdown adapter)

Customer Reviews

Based on 5 reviews
High quality product.

Fit and finish is excellent. The mirror is beautiful it doesn't cause any visible changes or light lost to the naked eye. Mounting is nice and clean and the twist lock works really well.

A beast of a diagonal.

This diagonal easily held my 2” Powermate and massive 32mm Luminos eyepiece solidly. A good spend.

Twist lock

This dielectric diagonal with twist lock feature is great. 99 percent reflection of mirror plus the twist lock holds your eyepieces firmly and well aligned and much easier to use than thumbscrews.


Its a great diagonal. well designed and versatile.


This is mounted on a C8. It's very heavy so balance could be an issue on smaller scopes. Machining is good with tight tolerances. The 2" to 1.25" twist lock adapter works well and holds eyepieces inverted securely. To the eye, the image is very bright with no visible imperfections.

Why Should You Trust All Star Telescope?

We've Made All The Mistakes
So You Don't Have To

Learn More