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iOptron Dielectric Star Diagonal (1.25")

iOptron Dielectric Star Diagonal (1.25")

by iOptron
SKU IOP-6231
CA$111.00 - CA$111.00
CA$111.00
CA$111.00 - CA$111.00
CA$111.00
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  • 1.25" Barrel Diameter
  • Dielectric Mirror Coatings
  • Improves Image Brightness and Contrast
  • Durable, Long-Lasting Reflective Surface
  • Ideal for Refractors, SCTs, and Maksutov-Cassegrains
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  • Description
  • FAQ
  • Specifications
  • In the Box
  • Warranty

  • Dielectric Star Diagonal (1.25")

    The 1.25" Dielectric Star Diagonal is a critical upgrade for any telescope using a 1.25" focuser, employing advanced multi-layer coatings to deliver the brightest possible images to your eyepiece. It replaces standard aluminum or prism diagonals to maximize contrast on faint objects and ensure the diagonal's reflective surface lasts for years without degradation.

    Multi-Layer Dielectric Coatings: Preserving Your Telescope's Light

    Unlike standard aluminum mirror coatings that can tarnish and lose reflectivity over time, a dielectric diagonal uses dozens of micro-thin layers of optical material. This construction creates a highly reflective, scratch-resistant surface that maintains peak brightness and contrast for the life of the diagonal.

    This durability means you can clean the mirror surface with less risk of damage, and the diagonal will not degrade from exposure to humidity or airborne contaminants. The result is a consistently brighter view of faint deep-sky objects like the Orion Nebula (M42) or the Whirlpool Galaxy (M51) compared to what an aged, standard-coated diagonal can provide.

    Mirror vs. Prism: Why a Dielectric Diagonal Excels with Reflectors

    While both mirror and prism diagonals place the eyepiece at a comfortable 90° angle, their optical properties differ. A mirror diagonal is free from chromatic aberration, making it a superior choice for fast focal ratio telescopes (f/6 and below), where a simple prism can introduce false color on bright targets like Jupiter or the Moon.

    • Astronomical Orientation: This diagonal provides an image that is correct up-and-down but reversed left-to-right. This is the standard orientation for astronomical observing and star-chart matching.
    • Refractor and Cassegrain Use: It is the ideal choice for refractors, Schmidt-Cassegrain (SCT), and Maksutov-Cassegrain telescopes, preserving the light gathered by the primary optics without introducing optical errors. It is not intended for use with Newtonian reflectors.

  • What is the main advantage of a 1.25" Dielectric Star Diagonal over a standard diagonal?

    The primary advantages are longevity and sustained reflectivity. Dielectric coatings are far more durable than standard aluminum and will not tarnish or degrade over time, ensuring your views remain bright and high-contrast for many years.

    Is this 1.25" Dielectric Diagonal a good choice for my 8-inch f/10 SCT?

    Yes, it is an excellent choice. An 8" SCT gathers significant light, and a dielectric diagonal ensures that as much of that light as possible reaches your eyepiece. The 1.25" barrel is the standard size for the visual back on most SCTs, making it a direct fit.

    Will this diagonal introduce any color error when viewing Jupiter with my fast f/5 refractor?

    No. As a first-surface mirror system, this Dielectric Star Diagonal is entirely free of chromatic aberration (false color). This makes it optically superior to many prism diagonals when used with "fast" optical systems like short-tube refractors or astrographs.

    How do I clean the mirror on this 1.25" Dielectric Diagonal?

    While the dielectric coatings are very durable, you should always treat optical surfaces with care. First, use a blower bulb to remove any loose dust. If further cleaning is needed, use a dedicated optical cleaning solution and microfiber cloths, applying minimal pressure in a gentle, straight-line motion.

    Does this diagonal provide a "correct" image for terrestrial viewing?

    No. This diagonal provides an image that is upright (correct up-and-down) but mirror-reversed (flipped left-to-right). This is standard for astronomical use. For a fully corrected image for daytime terrestrial viewing, you would need an "erect image" or "correct image" prism diagonal.

    Will this 1.25" diagonal fit the focuser on my telescope?

    This diagonal is designed to fit any telescope equipped with a 1.25" focuser or visual back. This includes the vast majority of refractors, Schmidt-Cassegrains, and Maksutov-Cassegrains on the market. It is not compatible with 2" focusers without a step-down adapter.

  • Type Dielectric Mirror Star Diagonal
    Barrel Size 1.25"

    • 1.25" Dielectric Star Diagonal

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  • David Astro General Accessory Warranty