Used Stellarvue 1/10th wave Dielectric Star Diagonal, 2” With Twist-Lock

SKU: U2205-DP-D1028ECF

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  • $109.00
  • Regular price $159.00

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Not Returnable Please note that used items are not returnable.

This is a terrific 2" 99% dielectric diagonal, with a flatness to 1/10th of a wave, in excellent condition.  It is less than 2 years old and is completely clean. 


This diagonal uses a thick, over-sized mirror polished to 1/10th wave with protective, dielectric coating with 99% reflectivity. The body has carbon fiber sides. It has a collet type twist lock on the 2" eyepiece tube and the deluxe 1.25" compression ring adapter is included. Both the two inch insert tube and adapter have filter threads. These diagonals are double tested at Stellarvue for perfect alignment and performance.

Star diagonals are a critical component of any telescope. The performance of an otherwise excellent telescope can be seriously compromised using a diagonal that is misaligned or pinched. Each diagonal and erecting prism we sell is tested for alignment and will preserve the exceptional quality of your telescope.

The D1028 uses a twist lock collet. Rotate the twist lock lever counter-clockwise to open. Insert the 1.25” adapter or 2” eyepiece and then rotate the lever clockwise to tighten.

The two inch insert tube has filter threads and a safety taper that will more accurately seat the diagonal and tend to keep it from falling out accidentally. Make sure you tighten the lock screw(s) when installing the diagonal in a focuser.

The diagonal comes with a 1 1/4” adapter allowing you to use 1 1/4” eyepieces. The adapter uses a compression ring and has an insert safety groove and filter threads. We do not use a twist lock lever on the 1 1/4" adapter since it is more difficult to use. Some Barlows have a long insert tube. Always check before using them to make sure they do not strike the mirror. The 2" female insert tube on this diagonal will accept 41mm or 1.61" of nose piece length before hitting the built in safety stop. If your 2" nose piece is longer than this specified distance, the nose piece will not fully insert, though this is rarely an issue. The D1028ECF adds 4.1" or 104mm to the optical path.

The thick mirror is easier to access for cleaning. Simply remove the siz screws using a 2 mm Allen wrench and pull off the carbon fiber side plates. Push on one side of the mirror and it will slide out the other side.

Hold the mirror only by the back and edges. Never touch the surface. Remove the loose dust from the surface with air from a bulb syringe or bulb blower such as a “Rocket Blower.” Using a soft camel hair brush about 1’ wide while blowing with the bulb blower will help remove particles.

Never blow on the surface as your breath, canned air or from an air compressor as moisture drops will spot the surface.

Once you have removed particles, apply reagent grade acetone to a lens cloth. Gently and very slowly draw the cloth across the mirror. Do not apply too much pressure when wiping the surface or you will scratch the mirror or coating. Follow precautions necessary when using acetone. Be advised that in cleaning the mirror, you will not end up with a pristine surface if you wipe too fast. With time you will learn how to avoid streaks. Some residual streaks may remain so only do this cleaning if necessary.


  • 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
  • Multiple layers of dielectric coatings provide an over 99% reflective surface, ensuring the maximum amount of light collected by the telescope reaches the eyepiece
  • 1/10th wave mirror is optically flatter than other diagonal mirrors, which are usually rated to 1/4 wave
  • 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
  • Ensure maximum light transmission without loss of optical quality with the Stellarvue Dielectric Star Diagonal with Twist-Lock. Upgrade your existing star diagonal to this premium one and enjoy brighter, sharper images without replacing your telescope.


With all its features and these high-end finishes, the Stellarvue 1/10th wave Dielectric Star Diagonal, 2” with Twist-Lock is one of the highest quality 2" star diagonals ever offered.

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.