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Thread adapters

ECSiNG M48 to M42 double-male adapter

An anodised aluminium ring with M48 × 0.75 and M42 × 0.75 male threads, blackened inside, containing no optical element at all.

ECSiNG M48 to M42 adapter ring in black anodised aluminium

ECSiNG M48 to M42 double-male adapter

An anodised aluminium ring with M48 × 0.75 and M42 × 0.75 male threads, blackened inside, containing no optical element at all.

Reduction factor
Not published by the maker.
Required back focus
Not published by the maker.
Image circle
Not published by the maker.
Corrector function
Not published by the maker.
Thread standards
M48 × 0.75 and M42 × 0.75, both male
Vignetting
Not published by the maker.
Housing
Aluminium, black anodised, matt internal wall
Amazon reference
B0C773T289 (same reference on 5 Amazon marketplaces)
EAN
4895243556683
  • Both threads named with their pitch
  • A matt bore, which reduces the reflections a shiny adapter introduces
  • It reduces nothing: the category is wrong and this page says so

Best for: Joining a female M48 component to a female T2 one

≈ £10 / €12
Check price on Amazon

Specifications

Reduction factor
Not published by the maker.
Required back focus
Not published by the maker.
Image circle
Not published by the maker.
Corrector function
Not published by the maker.
Thread standards
M48 × 0.75 and M42 × 0.75, both male
Vignetting
Not published by the maker.
Housing
Aluminium, black anodised, matt internal wall
Amazon reference
B0C773T289 (same reference on 5 Amazon marketplaces)
EAN
4895243556683

Not a reducer

There is no glass in it. It is an aluminium ring with a thread on each face, and it is filed among focal reducers because that is where the listing sits — not because of anything it does optically. A reader ordering a reducer and receiving this would have lost an evening.

What it is good for

Joining an M48 female thread to a T2 female thread. That is a real junction in an imaging train, and a ring that does it in one piece is better than two stacked adapters.

The matt bore

The inner wall is blackened matt. Close to the focal plane, a shiny internal surface bounces light back into the image and flattens contrast. Few adapter listings mention it; this one does.

The number that would finish it

Length. “Minimum mechanically possible” is a description, not a measurement, and every millimetre in the train is subtracted from the back focus a reducer demands.

Availability

German, French, Italian and Spanish Amazon stores ran from 12 € to 14 € on the day of the survey.

British Amazon store lists it in local currency, which the euro range above sets aside.

American Amazon store gave no result whatever, so the buy button there opens a search rather than an empty page.

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 focal reducers

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    Oumij1 0.5x reducer, M28.5 × 0.6

    A 0.5x reducer for 1.25 in eyepiece noses in an aluminium housing, with the same stated exclusions as its twin listing.

    Reduction factor
    0.5x, per the maker
    Required back focus
    Not published by the maker.
    Image circle
    Not published by the maker.
    Corrector function
    Focal reducer with optics
    Thread standards
    M28.5 × 0.6 — the standard 1.25 in filter thread · Screws onto the nose of a 1.25 in eyepiece
    Vignetting
    Not published by the maker.
    Housing
    Aluminium alloy
    Amazon reference
    B093ZSLSDJ (same reference on 4 Amazon marketplaces)
    EAN
    9182438203992
    • The thread is named correctly, which several neighbours on this shelf fail to do
    • The exclusions are published rather than discovered
    • Shares its entire description with another listing

    Best for: A second reducer, or a first one where price decides

    ≈ €21
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  • Skyoptikst f/6.3 reducer-corrector with SCT thread

    Skyoptikst f/6.3 reducer-corrector for SCT

    A four-element fully multi-coated reducer-corrector that threads onto the rear cell of a Schmidt-Cassegrain and converts f/10 to f/6.3.

    Reduction factor
    f/10 to f/6.3, as the maker states it
    Required back focus
    The listing gives none
    Image circle
    Not published by the maker.
    Corrector function
    Reducer and field corrector with optics — four elements
    Thread standards
    Schmidt-Cassegrain rear thread
    Vignetting
    Not published by the maker.
    Housing
    Fully multi-coated, per the maker · Aluminium alloy; all optical glass elements per the maker
    Amazon reference
    B0CN9CVSBP (same reference on 6 Amazon marketplaces)
    EAN
    0741754671657
    • Four elements correct the field as well as reducing, which a two-element reducer does not
    • The conversion is published as a pair of focal ratios rather than as a bare factor
    • The required distance to the sensor is not published, and a reducer has no tolerance on it

    Best for: A Schmidt-Cassegrain used for imaging, where f/10 makes exposures impractically long

    ≈ $95 / £93 / €109
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  • VBESTLIFE 0.5x focal reducer in aluminium housing

    VBESTLIFE 0.5x reducer, M28.5 × 0.6

    A 0.5x reducer threading onto the nose of a 1.25 in eyepiece, which the maker states is not recommended for very fast telescopes or wide-angle eyepieces.

    Reduction factor
    0.5x, per the maker
    Required back focus
    Not published by the maker.
    Image circle
    Not published by the maker.
    Corrector function
    Focal reducer with optics
    Thread standards
    M28.5 × 0.6 — the standard 1.25 in filter thread · Screws onto the nose of a 1.25 in eyepiece
    Vignetting
    Not published by the maker.
    Housing
    Aluminium alloy
    Amazon reference
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    EAN
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    • The thread is named correctly as M28.5 × 0.6
    • The maker states what it is not suitable for, which is unusually honest
    • The bullet text is shared verbatim with another seller’s listing

    Best for: Widening the field of a long-focal-length telescope with a narrow-field eyepiece

    ≈ £12 / €20
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The rest of this rack

  • Celestron 94107 variable polarising moon filter

    Celestron Variable Polarizing Moon Filter (94107)

    A two-element polarising filter for 1.25 in eyepieces with transmission adjustable from 1 to 40 per cent by rotating its lower ring.

    Transmission percentage
    1 % to 40 %, adjustable, as the maker publishes it
    Neutral or tinted dimming
    Not published by the maker.
    Fixed or variable design
    Variable polarising filter, threaded for 1.25 in eyepieces · Rotate the lower ring, per the maker · Threaded on both faces, so other filters can be combined with it
    Thread size
    Not published by the maker.
    Glass flatness
    Not published by the maker.
    Cell depth
    Not published by the maker.
    Amazon reference
    B07N99RW5K (same reference on 6 Amazon marketplaces)
    EAN
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    • A published transmission range rather than a single fixed figure or a colour word
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    ≈ $43 / £42 / €38
    Check price on Amazon
  • Omegon Premium 2 inch moon filter with 25 per cent transmission

    Omegon Premium Moon Filter 25 % 2 in

    A neutral grey Moon filter passing 25 per cent of the light, threaded for 2 in eyepieces, intended to dim the Moon without tinting it.

    Transmission percentage
    25 %, as the maker publishes it
    Neutral or tinted dimming
    Neutral — the Moon keeps its natural appearance, per the maker
    Fixed or variable design
    Neutral grey filter, threaded for 2 in eyepieces
    Thread size
    2 in filter thread
    Glass flatness
    Not published by the maker.
    Cell depth
    Not published by the maker.
    Amazon reference
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    EAN
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    • The transmission is published as a percentage rather than a word
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    A plane-parallel Moon filter that screws into 1.25 in eyepieces, sold on the quality of its substrate rather than on a stated transmission.

    Transmission percentage
    The listing gives none anywhere in the listing
    Neutral or tinted dimming
    Not published by the maker.
    Fixed or variable design
    Moon filter, threaded for 1.25 in eyepieces
    Thread size
    Not published by the maker.
    Glass flatness
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    Cell depth
    Not published by the maker.
    Amazon reference
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    EAN
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All focal reducers