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IMPORTANT: Our store is located in Canada. All orders that include products manufactured outside of Canada or USA will be subject to tariffs and duties, regardless of the order value. US customers are responsible for all applicable duties and tariffs, and those will be billed by the carrier, except for the Lacerta upgrade kit, for which we collect them at checkout.
IMPORTANT: Our store is located in Canada. All orders that include products manufactured outside of Canada or USA will be subject to tariffs and duties, regardless of the order value. US customers are responsible for all applicable duties and tariffs, and those will be billed by the carrier, except for the Lacerta upgrade kit, for which we collect them at checkout.
Baader 90° Erecting Prism Diagonal - 2"
Baader 90° Erecting Prism Diagonal - 2"
Baader 90° Erecting Prism Diagonal - 2"
Baader 90° Erecting Prism Diagonal - 2"
Baader 90° Erecting Prism Diagonal - 2"
Baader 90° Erecting Prism Diagonal - 2"

Baader 90° Erecting Prism Diagonal - 2"

by Baader Planetarium
SKU BAA-2956152
$335.00 - $335.00
$335.00
$335.00 - $335.00
$335.00
Price Match Policy!
  • Provides a fully erect, non-reversed image
  • 90° viewing angle for comfortable observing
  • 2" barrel for use with large focusers
  • Includes a 2" to 1.25" reducer for eyepiece versatility
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  • Description
  • FAQ
  • Specifications
  • In the Box
  • Downloads
  • Warranty

  • Baader 90° Erecting Prism Diagonal - 2"

    The Baader 90° Erecting Prism Diagonal delivers a fully corrected, right-side-up and left-to-right correct image at a comfortable 90° angle, making it ideal for terrestrial viewing through an astronomical telescope. Its robust 2" barrel is designed to fit large focusers, enabling the use of wide-field eyepieces for expansive daytime landscapes or rich-field stargazing. For maximum flexibility, it includes a reducer for compatibility with the universally common 1.25" eyepiece format.

    A 90° Correct-Image View for Terrestrial and Astronomical Use

    Unlike standard star diagonals that produce a mirror-reversed image, an erecting prism corrects the view on both axes. This is essential for terrestrial applications like birdwatching or nature observation, where an upside-down or reversed image would be disorienting. For astronomical use, it provides an intuitive view that matches star charts, which is particularly helpful for beginners navigating the constellations or for public outreach.

    The 2" Format Advantage with a 1.25" Adapter

    The 2" barrel format allows the diagonal to accept eyepieces with the largest possible field stops, maximizing the true field of view your telescope can deliver. This is perfect for framing broad landscapes or sweeping through the Milky Way. The included high-quality 2" to 1.25" reducer ensures you can still use your entire collection of standard 1.25" eyepieces without needing to purchase a separate adapter, maintaining a secure and centered optical path.

    Baader Erecting Prism vs. a Standard 2" Mirror Diagonal

    Choosing between an erecting prism and a mirror diagonal involves a clear trade-off between image orientation and optical purity, especially for critical deep-sky imaging.

    • Erecting Prism (This Product): Its primary advantage is the fully corrected image, indispensable for terrestrial viewing. For casual astronomy, the convenience of a non-reversed view is significant. However, prisms can introduce a small amount of chromatic aberration, particularly in fast focal ratio telescopes (f/6 or below).
    • Mirror Diagonal: A high-quality mirror diagonal typically offers higher light transmission and superior color correction, making it the preferred choice for serious astronomical observing and astrophotography where every photon counts. Its drawback is the left-right reversed image, which is a non-issue for deep-sky objects but problematic for terrestrial use.

  • What is the primary use for the Baader 90° Erecting Prism Diagonal?

    Its main purpose is to adapt an astronomical telescope, such as a refractor or Schmidt-Cassegrain, for terrestrial daytime viewing. The prism corrects the image to be both upright and non-reversed, so landscapes, ships on the horizon, or wildlife appear as you would see them with binoculars.

    Can I use the Baader 2" Erecting Prism for observing planets and deep-sky objects?

    Yes, you can. It provides an intuitive, correctly-oriented view that is helpful for navigating with star charts. While a high-quality mirror diagonal is often preferred for critical deep-sky and planetary observation due to slightly better light transmission and color fidelity, this erecting prism is perfectly suitable for casual and educational astronomical viewing.

    Will the Baader 90° Erecting Prism Diagonal work with my Newtonian reflector telescope?

    No. Newtonian reflectors are not designed to use prism or mirror diagonals in their focusers. Adding one will prevent the telescope from reaching focus. This diagonal is designed for refractors, Schmidt-Cassegrains (SCTs), and Maksutov-Cassegrains (Maks).

    How does the Baader 2" Erecting Prism perform for birdwatching with a 100mm f/7 refractor?

    It performs exceptionally well in this scenario. A 100mm f/7 refractor is an excellent instrument for high-power terrestrial viewing, and this diagonal will provide a bright, sharp, and correctly oriented image. The 2" barrel allows the use of wide-field eyepieces to easily spot and track birds in flight, while the 1.25" adapter lets you switch to higher power for detailed views of plumage.

    Will I need an extension tube to reach focus with the Baader 90° Erecting Prism?

    Possibly. Prism diagonals often require more "in-focus" travel than mirror diagonals. While most modern refractors and SCTs have enough focuser travel to accommodate them, some older designs might not. If you find you cannot rack the focuser in far enough to achieve a sharp image, you may need to shorten your optical train.

    What is the advantage of the 2" barrel on the Baader Erecting Prism Diagonal?

    The 2" barrel allows the diagonal to accept 2" eyepieces, which can provide a much wider true field of view than 1.25" eyepieces. This is ideal for scanning large areas of the sky, like searching for the Andromeda Galaxy (M31), or for taking in wide terrestrial panoramas.

  • Diagonal Type Erecting Prism
    Viewing Angle 90°
    Barrel Size 2"
    Reducer Included 2" to 1.25"
    Net weight (kg) 0.56
    AR-Coating Multi-Coated (MC)
    Inner Diameter / Clear Aperture (mm) 38
    Optical length (mm) 99 mm with 2" barrel; with 1.25"-reducer additional 10 mm
    Inner Connection (eyepiece/-camera-sided) ø 1¼" (31.75 mm), ø 2" (50.8mm)
    Inner Connection (lens sided) M48
    Outer Connection (lens sided) ø 2" (50.8mm)
    Image Orientation Erect image, Non-reversed
    Reflection surface Total reflection

    • Baader 90° Erecting Prism Diagonal - 2"

      × 1

    • 2" to 1.25" Reducer

      × 1

    • Dust Caps

      × 2

  • Baader Planetarium Warranty