Skip to content
Price match 30-day returns* Talk to an astronomer before you buy
Celestron Dielectric Star Diagonal with Twist-Lock - 1.25"
Celestron Dielectric Star Diagonal with Twist-Lock - 1.25"
Celestron Dielectric Star Diagonal with Twist-Lock - 1.25"
Celestron Dielectric Star Diagonal with Twist-Lock - 1.25"
Celestron Dielectric Star Diagonal with Twist-Lock - 1.25"
Celestron Dielectric Star Diagonal with Twist-Lock - 1.25"

Celestron Dielectric Star Diagonal with Twist-Lock - 1.25"

by Celestron
SKU CEL-93571
$159.95 USD - $159.95 USD
$159.95 USD
$159.95 USD - $159.95 USD
$159.95 USD
Price Match Policy!
  • Over 99% reflectivity from 58-layer dielectric mirror coatings
  • 1.25” Twist-Lock holder provides a secure, self-centering grip
  • Diffraction-limited optics maintain your telescope's image quality
  • Machined aluminum housing with glare-threaded interior
  • Accepts standard 1.25" eyepiece filters
Backordered
Request Stock Alert
Availability Info
Qualifies for FREE Shipping in CONUS on orders over $350.
  • Description
  • FAQ
  • Specifications
  • In the Box
  • Downloads
  • Warranty

  • Celestron Dielectric Star Diagonal, 1.25” with Twist-Lock

    The Celestron Dielectric Star Diagonal, 1.25” with Twist-Lock, upgrades your telescope's optical train with a diffraction-limited BK7 mirror featuring 58 layers of dielectric coatings. These coatings achieve over 99% reflectivity, ensuring maximum light transmission for brighter, higher-contrast images. The diagonal weighs just 7.5 oz (212.6 g) and is housed in a durable, machined aluminum body measuring 4.5" x 2" x 3.5".

    99% Reflectivity from 58-Layer Dielectric Coatings

    The core of this diagonal is its BK7 mirror, which is coated with 58 layers of dielectric material to achieve over 99% reflectivity across the visual spectrum. Unlike standard aluminum or silver coatings that can degrade over time, these dielectric layers are highly durable and deliver consistently bright and sharp images. This ensures that the maximum amount of light collected by your telescope reaches your eyepiece, which is critical for observing faint deep-sky objects and resolving fine planetary detail.

    The 1.25" Twist-Lock Eyepiece Holder

    A significant upgrade from traditional thumbscrew holders, the Twist-Lock mechanism provides a secure, perfectly centered grip on any 1.25" eyepiece. A simple twist of the orange ring tightens a single compression ring, locking the eyepiece in place without scratching or marring its barrel. This self-centering action guarantees optimal opto-mechanical alignment, preserving the sharpness your telescope is capable of. An integrated barrel stop also prevents accessories with long barrels from making contact with the diagonal's mirror.

    Celestron Dielectric vs. Standard Diagonals: A Brighter Image

    A star diagonal is a critical component, and a lower-quality one can dim the view and degrade image quality. Standard aluminum diagonals typically offer 88-92% reflectivity, meaning a significant portion of the light from your telescope never reaches your eye. The Celestron Dielectric Star Diagonal, with its over 99% reflectivity, delivers a visibly brighter image. This upgrade alone can make the difference between detecting a faint galaxy's spiral arms or resolving subtle cloud bands on Jupiter.

    • Machined Aluminum Construction: The black anodized aluminum housing is built for durability and rigidity, preventing flexure that can misalign optics.
    • Glare Control: The interior of the 1.25" barrel is both glare-threaded and painted flat black to absorb stray light, maximizing image contrast.
    • Filter Compatibility: The barrel is threaded to accept standard 1.25" astronomy filters, allowing you to easily enhance views of the Moon, planets, and nebulae.

  • How will the Celestron Dielectric Star Diagonal improve views of Jupiter through my 8" SCT?

    An 8" SCT gathers a lot of light, and you want as much of it as possible to reach your eye. With over 99% reflectivity, this diagonal transmits more light than a standard one, making Jupiter's cloud belts and Great Red Spot appear brighter and with higher contrast. The diffraction-limited optics ensure you're seeing the full detail your telescope can resolve.

    Is the Twist-Lock holder on this diagonal secure enough for heavy 1.25" eyepieces?

    Yes. The Twist-Lock mechanism uses a single compression ring that applies even, firm pressure around the entire eyepiece barrel. This provides a more secure grip than a single thumbscrew, making it ideal for holding heavier, multi-element 1.25" eyepieces, even when the telescope is pointed at the zenith.

    Will the Celestron 1.25" Dielectric Diagonal work with my refractor telescope?

    Absolutely. This diagonal is designed for any telescope with a 1.25" focuser or visual back, including refractors, Schmidt-Cassegrains (SCTs), and Maksutov-Cassegrains (MCTs). It provides a more comfortable 90° viewing angle, which is especially useful for refractors when observing objects high in the sky.

    What is the advantage of 58-layer dielectric coatings over standard aluminum?

    Dielectric coatings are more reflective (over 99% vs. ~92% for enhanced aluminum) and far more durable. They are highly resistant to oxidation and cleaning, meaning the diagonal will maintain its peak brightness and contrast for many years, unlike aluminum coatings which can tarnish over time.

    Can I use 1.25" filters with the Celestron Dielectric Star Diagonal?

    Yes, the 1.25" nosepiece of the diagonal is threaded to accept standard 1.25" eyepiece filters. You can easily attach a Moon filter, a light pollution filter, or colored planetary filters before inserting the diagonal into your telescope's focuser.

    What does "diffraction-limited" optical quality mean for this diagonal?

    It means the mirror surface is smooth and accurate enough that it does not introduce any perceptible degradation to the image formed by the telescope. A diffraction-limited diagonal will pass the light through without adding aberrations, preserving the finest details your main optics can resolve.

  • Diagonal Size 31.75mm (1.25")
    Diagonal Type Mirror
    Glass Material BK7
    Coatings Dielectric, 58 layers
    Reflectivity Over 99%
    Optical Quality Diffraction limited
    Eyepiece Holder 1.25", Twist-Lock
    Compression Ring Yes, single ring
    Housing Construction Machined aluminum, black anodized
    Barrel Interior Glare threaded and painted flat black
    Filter Threads Yes, 1.25"
    Dimensions 114.3mm x 50.8mm x 88.9mm (4.5" x 2" x 3.5")
    Weight 7.5 oz (212.6 g)
    Telescope-Side Connection 1.25" barrel

    • 1.25” Dielectric Star Diagonal with Twist-Lock

      × 1

    • 1.25" Barrel Dust Cap

      × 1

    • 1.25" Eyepiece Holder Dust Cap

      × 1

  • Celestron 2-Year Warranty