Skip to content

Star diagonals

Celestron 1.25 in star diagonal (94115-A)

A 90-degree mirror diagonal for 1.25 in focusers, giving an image that is the right way up and reversed left to right.

Celestron 94115-A 1.25 inch star diagonal in black

Celestron 1.25 in star diagonal (94115-A)

A 90-degree mirror diagonal for 1.25 in focusers, giving an image that is the right way up and reversed left to right.

Mirror or prism construction
90-degree mirror star diagonal
Reflectivity
The listing does not carry it
Barrel size
1.25 in focuser and visual back
Clamping method
Standard 1.25 in eyepieces, Barlow lenses and accessories
Optical path length
Upright, with left and right reversed, as the maker states it
Build
Not published by the maker.
Amazon reference
B00009X3UO (same reference on 6 Amazon marketplaces)
EAN
0050234941150
  • The maker states the image orientation precisely instead of calling it “correct image”
  • Accepts everything with a 1.25 in barrel, including Barlows
  • No coating specification: dielectric, aluminium and enhanced aluminium all differ in reflectivity

Best for: A refractor or a Maksutov used visually, where looking up is otherwise uncomfortable

≈ $42 / €47
Check price on Amazon

Specifications

Mirror or prism construction
90-degree mirror star diagonal
Reflectivity
The listing does not carry it
Barrel size
1.25 in focuser and visual back
Clamping method
Standard 1.25 in eyepieces, Barlow lenses and accessories
Optical path length
Upright, with left and right reversed, as the maker states it
Build
Not published by the maker.
Amazon reference
B00009X3UO (same reference on 6 Amazon marketplaces)
EAN
0050234941150

What a star diagonal is for

It bends the light path through ninety degrees so the eyepiece points at the observer rather than away from them. On a refractor or a Maksutov aimed high, that is the difference between comfortable observing and lying on the ground.

The orientation, stated exactly

Upright, with left and right reversed. That is what a mirror diagonal does, and Celestron says so rather than using the looser phrase “correct image”. It means a chart has to be mentally flipped left to right while star-hopping.

The specification left blank

The mirror coating. Reflectivity is the whole performance of a diagonal, and the difference between a dielectric coating and plain aluminium is visible on faint objects. Nothing in the listing names it.

Where it must not be used

A Newtonian. Those instruments reach focus at the side of the tube already, and inserting a diagonal moves the focal plane beyond the eyepiece’s reach.

Availability

German, Italian and Spanish Amazon stores ran from 47 € to 65 € on the day of the survey.

American and British Amazon stores list it in local currency, which the euro range above sets aside.

French Amazon store stood above 1.6× the cheapest country. A gap that size normally means stock forwarded from abroad rather than a seller on the ground, so that figure is left out of the range above.

Figures as Keepa reported them on the day this page was last updated. Stock and pricing shift without warning.

Prices quoted in this text were read on 17 September 2026. The live price is at the top of the page.

What this fits

More star diagonals

  • Seben AP3 90 degree 1.25 inch star diagonal

    Seben AP3 90° star diagonal 1.25 in

    A 90-degree star diagonal with a 1.25 in fitting at both ends, explicitly excluded by the maker from use on Newtonian telescopes.

    Mirror or prism construction
    90-degree star diagonal · Not described — neither mirror nor prism is specified
    Reflectivity
    The listing does not carry it
    Barrel size
    31.7 mm (1.25 in) on both sides
    Clamping method
    Not published by the maker.
    Optical path length
    Not published by the maker.
    Build
    Refractors, Schmidt-Cassegrains and Maksutovs, as the maker lists them · Newtonian telescopes, stated outright by the maker
    Amazon reference
    B07NPC3SBN (same reference on 5 Amazon marketplaces)
    EAN
    4049467616306
    • The maker names both what it suits and what it does not, which is rare and useful
    • The least expensive diagonal on this shelf by a considerable margin
    • Neither the optical element nor its coating is described

    Best for: Replacing a missing or broken diagonal on a small refractor at minimum cost

    ≈ £6 / €6
    Check price on Amazon

The rest of this rack

  • EBTOOLS Canon EOS T-ring with 1.25 inch telescope coupling

    EBTOOLS T-ring and 1.25 in coupling for Canon EOS

    A set containing a Canon EOS T-ring and a 1.25 in to M42 coupling, with an inner ring that rotates to orient the camera.

    Camera mount
    A long list of Canon EOS and Rebel models is given in the first bullet
    T2 thread
    Not published by the maker.
    Flange distance
    Not published by the maker.
    Prime focus or projection design
    A T-ring for Canon EOS and a 1.25 in to M42 coupling, per the maker · 1.25 in (31.7 mm)
    Blackening
    Not published by the maker.
    Material
    Anodised aluminium
    Amazon reference
    B07JNSHWX7 (same reference on 5 Amazon marketplaces)
    EAN
    0757686467206
    • Both halves of the chain are supplied together, which is rarer than it should be
    • A rotating inner ring lets the camera be squared to the subject without unthreading
    • The compatibility list contains model names that do not resolve, such as “T4ki” and “Rebeliii1”

    Best for: A Canon EOS owner who wants both halves of the coupling in one purchase

    ≈ £15 / €16
    Check price on Amazon
  • SVBONY 1.25 inch M42 telescope camera projection adapter

    SVBONY 1.25 in M42 projection adapter

    A 1.25 in projection adapter with an extended 68 mm barrel carrying M42 × 0.75 threads on both the inside and the outside, fully threaded internally against reflections.

    Camera mount
    Canon EOS and Rebel SLR and DSLR with a T2 ring; the maker excludes EOS-M models
    T2 thread
    M42 × 0.75 both male and female
    Flange distance
    68 mm extended, as the maker publishes it
    Prime focus or projection design
    Projection adapter with an extension barrel · 1.25 in
    Blackening
    Fully threaded inside to minimise reflections, per the maker
    Material
    All metal aluminium
    Amazon reference
    B01LWJ2Z3Y (same reference on 5 Amazon marketplaces)
    EAN
    0608560842070
    • Publishes the barrel length, which is what enters the back focus calculation
    • Fully threaded inside, which is a stronger anti-reflection measure than matt paint
    • A 68 mm barrel consumes a great deal of focuser travel

    Best for: Eyepiece projection on a telescope with generous focuser travel

    ≈ £17 / €20
    Check price on Amazon
  • Walimex pro T2 to M42 mount adapter ring

    Walimex pro T2 adapter for M42 mount (23367)

    A mechanical transition ring letting T2-threaded telescopes and accessories be fitted to a camera with an M42 screw mount, with manual focus only.

    Camera mount
    T2 equipment onto an M42-mount camera — the reverse of a standard astronomy T-ring
    T2 thread
    The pitches of the two threads are not published
    Flange distance
    Not published by the maker.
    Prime focus or projection design
    Purely mechanical transition ring, per the maker
    Blackening
    Not published by the maker.
    Material
    Not published by the maker.
    Amazon reference
    B0C6DYVMGG (same reference on 6 Amazon marketplaces)
    EAN
    4056929233674
    • The maker is explicit that it carries no contacts and gives manual focus only
    • Names bellows and microscope adapters as well as telescopes
    • It goes the opposite way from a normal astronomy T-ring, which is easy to misread

    Best for: An M42 screw-mount camera body used with T2 astronomical or laboratory equipment

    ≈ £27 / €20
    Check price on Amazon

All star diagonals