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A telescope diagonal is a crucial accessory that redirects light from your telescope's optical tube to your eyepiece. This redirection allows for a more comfortable viewing angle, especially when observing objects high in the sky. Selecting the right diagonal can significantly enhance your astronomical experience by improving ergonomics and image quality.
Dielectric coatings; super flat mirror with dielectric coatings to reduce reflected light loss; provide an over 99% reflective surface; good for astronomical viewing
1.25 inches nosepiece fits 1.25 inches telescopes; accepts standard 1.25in filters; eyepieces; Barlow lenses and other accessories with a 1.25in insert barrel
90 degree viewing angle; diagonal reflects the telescope’s light path 90 degree to provide a more comfortable viewing angle; best for observing objects overhead
Correct upside down and left right reversed image; the view image is upright; but left and right reversed if use the 90 degrees to your telescope
Brass compression ring; Built in brass ring and thumbscrew accessories avoid eyepiece to rotate during adjustments; effortless fixes more firmly and will not scratch your eyepieces barrels
SV188P diagonal uses a high-reflective dielectric coating; more durable and more reflective than enhanced aluminum coating; reflectivity is up to 99%; for maximum field of view brightness and clarity
2-inch dielectric mirror diagonal; suitable for 2-inch telescopes and eyepieces; supports 2-inch filter installation; comes with a 2-inch to 1.25-inch converter; can be connected to 1.25-inch eyepieces; barlow and other telescope accessories
90 degree viewing angle; provides a more comfortable viewing angle to observe the starry sky above; provides an upright image; comfortable observation; reducing the steps of post-image processing
Star diagonal adopts a side screw locking design; there is a brass pressure ring inside the barrel; so that the eyepiece surface will not be damaged when locking the eyepiece; it has an eyepiece anti-contact block design; better protect your eyepiece from...
The interior of the SV188P has been specially treated to eliminate stray light; spray matte paint; the side burgundy cover is made of aluminum plate; and matte velvet is attached; it can effectively eliminate stray light; get a bright image
The diagonal is made of aluminum alloy; the lens uses a high-precision plane mirror with a 1/4 wavelength error; and the surface is coated with a dielectric film with a reflectivity of up to 99% to improve the performance of the reflector; the surface of...
Enhanced Aluminum Die; the SV221 diagonal mirror is designed with enhanced aluminum mold; which has higher light transmittance and clearer vision.
1.25 inches diameter; the SV221 diagonal mirror has a diameter of 1.25 inches; which can be applied to a 1.25 inches telescope and a 1.25 inches eyepiece.The image effect of this zenith mirror is positive up and down, and negative left and right.
With a brass pressure ring; the SV221 diagonal mirror has a brass pressure ring; which can prevent surface damage and scratch marks when the eyepiece is used with the SV221
Supports 1.25-inch filters features internal extinction treatment and supports the connection of 1.25-inch filters; Offering versatility for various observations
With filter thread; the SV221 diagonal mirror has M28.5x0.6mm filter thread; which supports the connection of 1.25 inches filter
90 degrees design; the SV221 diagonal mirror 90 degrees deflection angle design; you don't have to bend over when performing visual observation; and the observation experience is more comfortable
Internal extinction design; the SV221 diagonal mirror has internal extinction treatment; and the acquired image is clearer and brighter
90° Telescope Diagonal for Comfortable Viewing: Experience effortless astronomical observation with Telescope Diagonal Mirror featuring 90° angle design; Maintain an upright & comfortable posture, whether observing planets or terrestrial landscapes
Erect Image Diagonal with Amici Prism Technology: The integrated Amici Prism Diagonal BK7 optical glass corrects image orientation; delivering upright & non-reversed views—perfect for birdwatching and deep-sky exploration
Premium Fully-Coated Diagonal for Optimal Clarity: Multi-layer dielectric coatings on prisms and lenses ensure 89% reflection for a bright image; surpassing standard mirrors in brightness and sharpness for Star Diagonal applications
Resitant 1.25 Inch Telescope Diagonal Build: Combining an premium-grade aluminum barrel and impact-resistant ABS housing, this diagonal withstands extreme temperatures from -20°C to 60°C while fitting all 1.25" focusers
Enhanced Compatibility & Versatility: Utilize the M28.5×0.6mm filter thread to attach 1.25 inch moon filters or nebula filters, expanding your telescope diagonal’s functionality across celestial and terrestrial targets
Control Engineering for Crisp Imagery: Internal glare-eliminating threads and dual rubber dust caps minimize glare and debris; ensuring to improve brightness of image and reduce dark edge formed
Sophisticated Aesthetics & Ergonomics: The high-gloss finish resists fingerprints and scratches, while the compact lightweight design ensures portability for field astronomy
Firm locking; SV223 diagonal mirror has a clicklock locking mechanism; just turn the clicklock to securely fix the accessory; ensuring the eyepiece is installed and used stably; not easy to fall off
Coating: 99% Reflectivity SV223 diagonal mirror has metal high reflective dielectric coating
Surface accuracy: 1/10λ
High-quality machining out of the aluminum; SV223 star diagonal is composed of High-quality aluminum elements; chic; light and stable; internal antireflection baffling for highest contrast
90 degrees design; SV223 star diagonal has a 90 degrees refraction angle; providing a better observation experience when visually observing
Enhanced Viewing Comfort & Optical Performance: Features 90-degree observing angle for comfortable overhead viewing without neck strain; Premium multi-coated lenses maximize light transmission for exceptional clarity; Advanced internal extinction...
Universal Compatibility & Secure Mounting: Designed for 1.25 inch refracting telescopes with dual installation options including threaded and barrel mounts; The precision-engineered housing ensures secure eyepiece attachment without surface damage...
Precision Engineering & Durable Construction: Built with enhanced aluminum housing for superior light transmittance and long-term durability; Features precise 90-degree deflection angle providing erect images with lateral inversion; The sturdy...
User-Friendly Design & Easy Installation: Quick-install design with fixing eyepiece thumbscrew for safe and efficient accessory mounting; Specifically engineered for refracting telescopes with 1.25 inch fittings; The ergonomic viewing position eliminates...
Professional Features for Enhanced Observation: Provides vertically erect images with lateral inversion for stable astronomical viewing; Superior optical performance with advanced coatings and professional-grade materials; Ideal for both beginner and...
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
Accepts standard eyepieces, Barlow lenses, threaded filters, and other accessories with a 1. 25” Barrel
UNBEATABLE WARRANTY & SUPPORT: Buy with confidence from Celestron, a leading telescope brand in California since 1960. Your purchase includes a 2-Year US Warranty and unlimited support from our team of US-based experts.
1.25 Inch Diagonal Mirror: Compatible with 1.25in eyepieces and telescopes. Designed specifically for refractors telescopes and not suitable for reflector telescopes.
90 Degree Angle: The 90 degree diagonal mirror, when used with a refracting telescope, allows for upright images. Although left right reversed, it does not affect astronomical observations.
Fully Coated Lens: Fully coated lens come with dust cover, keep your lens clean for superior image fidelity.
Easy Installation: The refractor telescope diagonal mirror is easy to install and use. It inserts into the telescope with a 1.25in end and secures the 1.25in eyepiece with a screw.
Durability: 90 degree diagonal mirror is constructed of metal, plastic materials, sturdy and not easy to damage.
Last update on 2026-07-17 / Affiliate links / Images from Amazon Product Advertising API
How to Choose the Best Telescope Diagonals
Choosing the Right Diagonal
When selecting a telescope diagonal, consider these key factors to ensure optimal performance and comfort for your stargazing sessions.
Prism Type: The most common types are Amici prisms (image-correcting, suitable for terrestrial viewing) and mirror diagonals (typically offering slightly sharper images for astronomy). For purely astronomical use, a mirror diagonal is often preferred.
Barrel Size: Diagonals come in standard barrel sizes, usually 1.25-inch or 2-inch. Ensure the diagonal's barrel size matches the focuser of your telescope and the diameter of your eyepieces for compatibility. A 2-inch diagonal generally offers a wider field of view and is compatible with 1.25-inch eyepieces via an adapter.
Build Quality and Coatings: Look for diagonals with high-quality optical coatings, such as dielectric or enhanced aluminum coatings on mirrors, and anti-reflective coatings on prisms. These coatings minimize light loss and internal reflections, leading to brighter and sharper images. A sturdy construction ensures durability and proper alignment.
Frequently Asked Questions
What is the primary function of a telescope diagonal?
A telescope diagonal redirects the light path from the telescope's optical tube by 90 degrees. This allows for a more comfortable viewing position, particularly when observing celestial objects that are high overhead.
Are there different types of diagonals for different uses?
Yes, there are mirror diagonals and prism diagonals. Mirror diagonals are generally preferred for astronomical observation due to their efficiency, while prism diagonals (like Amici prisms) provide an upright, correctly oriented image suitable for terrestrial viewing.
What does 'barrel size' mean for a diagonal?
The barrel size refers to the diameter of the end that inserts into the telescope's focuser and holds the eyepiece. The most common sizes are 1.25-inch and 2-inch, and you need to match this to your telescope's focuser and eyepiece collection.
How do optical coatings affect a diagonal's performance?
High-quality optical coatings, such as dielectric or enhanced aluminum, minimize light loss and maximize reflectivity on mirrors. Anti-reflective coatings on prisms reduce internal reflections. These coatings result in brighter, sharper, and higher-contrast images.
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