Best Star Diagonals for Comfortable Viewing (2026)
Updated How we research
Celestron 93573 Dielectric Star Diagonal 2 inch with Twist Lock and 2 inch to 1.25 inch Step-Down Adapter
Celestron 93573 2 inch dielectric star diagonal with twist lock and 2 inch to 1.25 inch step-down adapter.
Celestron Dielectric Star Diagonal 1.25 inch with Twist Lock 58 Layer Coating 99% Reflectivity
Celestron 1.25 inch dielectric star diagonal with twist lock and 58 layer coating for 99% reflectivity.
A star diagonal bends the light path 90 degrees so you look down into a refractor or SCT instead of crouching behind it. The two types are dielectric mirror diagonals, which offer very high reflectivity and neutral color, and prism diagonals, which can give excellent contrast in smaller scopes. Check the barrel size, 1.25 inch or 2 inch, whether it fits your focuser or SCT thread, and that it produces a correct right-side-up but mirror-reversed image, standard for astronomy. Star diagonals suit refractor, SCT, and Maksutov owners who want a comfortable viewing angle for targets high in the sky. A practical tip: a quality 2 inch dielectric diagonal with a 1.25 inch adapter covers both eyepiece sizes and loses almost no light, making it a good long-term buy. If you also glance at terrestrial scenery, consider an erecting prism diagonal that corrects the left-right flip for a natural daytime view.
The short version
We compared 7 picks. Our scores range from 8.0 to 8.8 out of 10.
- Best overall:Celestron 93573 Dielectric Star Diagonal 2 inch with Twist Lock and 2 inch to 1.25 inch Step-Down Adapter. Highest overall score in this guide at 8.8/10.
- Also great value:SVBONY SV188P Telescope Diagonal, 2" 90°Mirror Diagonal 99% Reflectivity. Value score of 9/10, overall 8.4/10.
- Solid build:Celestron Dielectric Star Diagonal 1.25 inch with Twist Lock 58 Layer Coating 99% Reflectivity. Build and materials score of 8/10, overall 8.6/10.
- Feature-rich:SVBONY SV223 90 Degree Diagonal Mirror 99% Reflective Dielectric Star Diagonal 2 inch with 1.25 Adapter. Features score of 8/10, overall 8.4/10.
Scores are our editorial assessment, not customer ratings. How we score
- 1.Celestron 93573 Dielectric Star Diagonal 2 inch with Twist Lock and 2 inch to 1.25 inch Step-Down Adapter8.8/10See on AmazonCheck price
- 2.Celestron Dielectric Star Diagonal 1.25 inch with Twist Lock 58 Layer Coating 99% Reflectivity8.6/10See on AmazonCheck price
- 3.SVBONY SV188P Telescope Diagonal, 2" 90°Mirror Diagonal 99% Reflectivity8.4/10See on AmazonCheck price
- 4.SVBONY SV223 90 Degree Diagonal Mirror 99% Reflective Dielectric Star Diagonal 2 inch with 1.25 Adapter8.4/10See on AmazonCheck price
- 5.SVBONY SV188P Telescope Diagonal 1.25" 90°Mirror Diagonal 99% Reflectivity8.1/10See on AmazonCheck price
- 6.Astromania Telescope Diagonal 2" 90° Diagonal Mirror 99% Reflective Coating8.0/10See on AmazonCheck price
- 7.SVBONY SV223 1.25” Telescope Diagonal, 90 Degree Dielectric Mirror8.0/10See on AmazonCheck price
#1Celestron 93573 2 inch dielectric star diagonal with twist lock and 2 inch to 1.25 inch step-down adapter.
Fit for the job 9/10 · Features and specs 9/10 · Build and materials 9/10 · Value 8/10
- + Step-down adapter supports both 2 inch and 1.25 inch eyepieces
- + Twist lock secures heavy eyepieces safely
- + Dielectric coating provides bright, contrasty views
- - Heavier than 1.25 inch diagonals, so small refractors may tip on light mounts
- - Premium price compared with budget 2 inch diagonals
#2Celestron 1.25 inch dielectric star diagonal with twist lock and 58 layer coating for 99% reflectivity.
Fit for the job 9/10 · Features and specs 9/10 · Build and materials 8/10 · Value 8/10
- + 58 layer dielectric coating reaches 99% reflectivity for bright views
- + Twist lock holds eyepieces securely without marring barrels
- + Celestron quality suits refractors and SCTs
- - Priced above basic diagonals with similar coating claims
- - Small-barrel format rules out wide-field 2 inch eyepieces
#3SVBONY's SV188P 2 inch, 90-degree dielectric diagonal with reflectivity stated at up to 99% and a 2 inch to 1.25 inch adapter included. A budget way into 2 inch wide-field eyepieces.
Fit for the job 9/10 · Features and specs 8/10 · Build and materials 7/10 · Value 9/10
- + Dielectric coating with reflectivity up to 99%, described as more durable than an enhanced aluminum coating
- + Comes with a 2 inch to 1.25 inch converter and supports 2 inch filters, so both eyepiece sizes work
- + Brass pressure ring protects eyepiece barrels, and the interior is matte treated to cut stray light
- - Uses a side screw lock, not the twist-lock collar found on the pricier diagonals in this guide
- - Mirror accuracy is stated as 1/4 wavelength, a looser figure than premium diagonals quote
#4SVBONY SV223 90 degree 2 inch dielectric star diagonal, 99% reflective, with 1.25 adapter.
Fit for the job 9/10 · Features and specs 8/10 · Build and materials 7/10 · Value 9/10
- + 99% reflective dielectric coating delivers bright views
- + 1.25 adapter provides compatibility with smaller eyepieces
- + Affordable 2 inch upgrade for refractors and SCTs
- - Build finish may not match Celestron or Orion diagonals
- - Larger size adds weight to small telescopes
#5A 1.25 inch, 90-degree dielectric mirror diagonal with a stated reflectivity of over 99%. A low-cost upgrade for the diagonal on small refractors and Cassegrains with a 1.25 inch focuser.
Fit for the job 9/10 · Features and specs 7/10 · Build and materials 7/10 · Value 9/10
- + Dielectric coatings on a super-flat mirror reduce reflected light loss, with the surface stated at over 99% reflective
- + 1.25 inch nosepiece accepts standard 1.25 inch filters, and the body takes 1.25 inch eyepieces and Barlow lenses
- + Brass compression ring with thumbscrew holds the eyepiece firmly without scratching the barrel
- - 1.25 inch format only, so it cannot take 2 inch wide-field eyepieces on a larger focuser
- - The view is upright but reversed left to right, as the listing notes, which is normal for a mirror diagonal
#6A 2 inch, 90-degree dielectric mirror diagonal with a stated 99% reflectivity and a Pyrex glass mirror. It ships with an SCT adapter and a 2 inch to 1.25 inch adapter for refractors and Cassegrains.
Fit for the job 9/10 · Features and specs 8/10 · Build and materials 8/10 · Value 6/10
- + Multi-layer dielectric coatings on a super-flat Pyrex mirror, with reflectivity stated at over 99% for brighter images
- + Includes both an SCT to 2 inch adapter and a 2 inch to 1.25 inch adapter, so it takes both eyepiece sizes
- + Listed as suitable for refractors, Schmidt-Cassegrains, ACF, EdgeHD and Maksutov-Cassegrain telescopes
- - The listing says it is not recommended for reflectors, especially Newtonians, so it is no use on a Dobsonian
- - Costs about twice as much as the budget 2 inch dielectric diagonal in this guide for the same stated reflectivity
#7A 1.25 inch, 90-degree dielectric diagonal with a clicklock collar and a coating stated at 99% reflectivity. For observers who swap eyepieces often on a 1.25 inch focuser.
Fit for the job 9/10 · Features and specs 8/10 · Build and materials 8/10 · Value 6/10
- + Clicklock mechanism clamps the eyepiece with a fast locking action for a stable, secure fit, per the listing
- + Thick precision optical flat mirror with an enhanced dielectric coating stated at 99% reflectivity
- + Aluminum body with internal antireflection baffling and a brass compression ring to protect eyepiece barrels
- - Priced well above basic 1.25 inch dielectric diagonals, so the clicklock collar is what you are paying for
- - 1.25 inch only: wide-field 2 inch eyepieces need a 2 inch diagonal and focuser instead
Before you buy: trade-offs we flagged
No pick is perfect. These are the main compromises we noted for the top products in this guide, so you can check they will not matter for you.
- Heavier than 1.25 inch diagonals, so small refractors may tip on light mounts (Celestron 93573 Dielectric Star Diagonal 2...)
- Priced above basic diagonals with similar coating claims (Celestron Dielectric Star Diagonal 1.25 inch...)
- Uses a side screw lock, not the twist-lock collar found on the pricier diagonals in this guide (SVBONY SV188P Telescope Diagonal, 2"...)
- Build finish may not match Celestron or Orion diagonals (SVBONY SV223 90 Degree Diagonal Mirror 99%...)
- 1.25 inch format only, so it cannot take 2 inch wide-field eyepieces on a larger focuser (SVBONY SV188P Telescope Diagonal 1.25"...)
- The listing says it is not recommended for reflectors, especially Newtonians, so it is no use on a Dobsonian (Astromania Telescope Diagonal 2" 90° Diagonal...)
Frequently asked questions
›What is the best choice among star diagonals for comfortable viewing (2026)?
Celestron 93573 Dielectric Star Diagonal 2 inch with Twist Lock and 2 inch to 1.25 inch Step-Down Adapter is our top overall pick. Celestron 93573 2 inch dielectric star diagonal with twist lock and 2 inch to 1.25 inch step-down adapter. It earns our score of 8.8/10, based on fit for the job, features, build and value.
›What is a good budget option?
Celestron Dielectric Star Diagonal 1.25 inch with Twist Lock 58 Layer Coating 99% Reflectivity is the strongest low-cost pick in this guide. Celestron 1.25 inch dielectric star diagonal with twist lock and 58 layer coating for 99% reflectivity.
›How much should I expect to spend?
Picks in this guide span See on Amazon price bands (roughly: $ = under $30, $$ = $30 to $100, $$$ = over $100). We never display exact prices because they change constantly, so the buttons above always show Amazon's current price.
›How were these products chosen?
We shortlist products that fit the job this guide solves and compare their published specifications, such as size, capacity, materials and what is included. Each pick gets an editorial score out of 10 for fit, features, build and value, and we write the pros and cons from those details. Our score is not an Amazon customer rating. We earn a commission if you buy through our links, which never affects the ranking.
Stargazer Nest independently selects every product; we may earn a commission from links above.
Popular right now
- Best Intervalometers for Automated Astro Shots (2026)Buying guide
- Best Finder Scopes to Locate Targets Fast (2026)Buying guide
- Telescope Aperture and Magnification ChartArticle
- Best Red Flashlights to Protect Night Vision (2026)Buying guide
- Equatorial mount explainedGlossary
- Best GoTo Mounts for Automated Object Finding (2026)Buying guide
Based on the last 28 days of search and visitor data.