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.
Looking for the best Telescope Diagonals?
Discover now our comparison of the best Telescope Diagonals. It is never easy to choose from the wide range of offers. On the market, you will find an incalculable number of models, all at different prices. And as you will discover, the best Telescope Diagonals are not always the ones at the highest prices! Many criteria are used, and they make the richness and relevance of this comparison.
To help you make the best choice among the hundreds of products available, we have decided to offer you a comparison of the Telescope Diagonals in order to find the best quality/price ratio. In this ranking, you will find products listed according to their price, but also their characteristics and the opinions of other customers. Also discover our comparisons by categories. You won’t have to choose your products at random anymore.
SaleNo. 1
SVBONY SV188P Dielectric Mirror Star Diagonal, 90 Degree Mirror Diagonal, 99% Reflectivity Dielectric Coatings...
- 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
No. 2
SVBONY SV188P Dielectric Mirror Star Diagonal, 90 Degree Mirror Diagonal, 99% Reflectivity Dielectric Coatings...
- 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...
SaleNo. 3
Astromania 1.25 Inch Telescope Diagonal with Amici Erecting Prism - 90° Fully-Coated Star Diagonal for...
- 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
No. 4
SVBONY SV221 90 Degree Diagonal Mirror, Telescope Diagonal 1.25 inches with Brass Compression Rings, Telescope...
- 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
SaleNo. 5
SVBONY SV223 90 Degree Diagonal Mirror, 99% Reflective Dielectric Coating Erect Image Star Diagonal 2 Inches...
- 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
SaleNo. 6
CELESTRON Dielectric Star Diagonal 1.25" with Twist Lock
- 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.
−9%
$144.95
Buy On Amazon
SaleNo. 7
SVBONY SV188 Dielectric Mirror Star Diagonal 1.25 inch 90 Degree Fully Metal for Refracting Telescope Eyepiece...
- The 90% reflectivity flat mirror can reduce light loss and make the field of view clearer and sharper
- Standard 1.25 inches diameter can be used with 1.25 inches telescope accessories such as eyepieces and barlow lens
- 90 degree viewing angle; provide a more comfortable observation angle to observe the stars above the head
- Compatible with refractors and catadioptric telescopes; not suitable for reflector telescopes
- Body material is full metal; With dust cover always keep your lens clear prolong life
No. 8
CelticBird 0.965Inch Telescope Accessory Kit for 0.965 Telescope - Comes with Four Eyepieces...
- It contains 4mm/6mm/12.5mm/ 20mm eyepiece, a 2x berlow lens and 90 degree diagonal.
- Barlow lens —— A visual Barlow, doubles the magnification of any inserted 0.965 inch eyepiece.
- 4mm/6mm/12.5mm/ 20mm eyepieces ——for different power in any telescope.
- This six-piece 0.965inch astronomy accessory kit let you get the most out and enhances the performance of your telescope.
- A 90 degree diagonal.
SaleNo. 9
SVBONY SV221 Diagonal Mirror 1.25 inches, 45-Degree Correct-Image Prism Diagonal Provides Sharp Views that are...
- Clear views; 45-degree correct-image prism diagonal provides sharp views
- Innovative design; the main mirror housing is made of precision molded ABS plastic. The end connecting to the eyepiece is made of plastic, while the other end is made of aluminum alloy.
- Brass lock screw and compression rings; equipped with brass lock screw and compression rings for precise connection and protection against scratches and damages
- Supports 1.25-inch filters; featuring multi-coated (MC) surfaces; and supports the connection of 1.25-inch filters for versatile observations
- Erect Image observation; provides erect image observation without image inversion
- Full field coating; features multi-coating for comfortable viewing experience
- Clear Aperture; offers a clear aperture of 19mm; ensuring clear observation results
- Dustproof design; comes with a dustproof cover to keep the lens clean
- Screw clamping system; features a screw clamping system for secure and easy usage
- Wide compatibility; designed for refractor telescopes and some catadioptric telescopes like schmidt-cassegrain and maksutov-cassegrain; not compatible with newtonian/dob reflector telescopes
No. 10
Astromania Telescope Diagonal 2 Inch 90-Degree Diagonal Mirror 99% Reflective Dielectric Coating Erect Image...
- The 2 inch telescope diagonal features a 99 percent reflective surface; the optics are crafted from Pyrex glass; additionally; equipped with an SCT interface and a 1.25-inch adapter; significantly broadening the range of compatible telescopes and...
- Multi Layered Dielectric Coatings: Dielectric coatings on the super-flat mirror reduce reflected light loss; providing a surface with over 99% reflectivity for brighter and harper images; which is highly beneficial for astronomical observations
- Wide Compatibility: Suitable for refractors included Schmidt-Cassegrains; ACF; EdgeHD and Maksutov-Cassegrains; it can be connected to other eyepieces; barlow lens and filters; among other accessories; via a 1.25-inch adapter
- 90 Degrees Design: The Astromania 2 inch 90-Degree 99% Dielectric Diagonal Mirror adopts a 90 degrees design; which can provide you with a better observation experience during visual observation
- Premium Aluminum Material: It is constructed from aluminum alloy; which significantly enhances the star diagonal longevity; equipped with brass compression ring; non-marring compression safety secures the eyepieces
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Last update on 2026-04-17 / 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.