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Thread adapters

ECSiNG M48 male to M42 male adapter

A male-to-male ring joining M48 × 0.75 to M42 × 0.75 with the shortest possible mechanical length, blackened inside against reflections.

ECSiNG M48 to M42 double-male adapter ring

ECSiNG M48 male to M42 male adapter

A male-to-male ring joining M48 × 0.75 to M42 × 0.75 with the shortest possible mechanical length, blackened inside against reflections.

Slot count and filter size
M48 × 0.75 and M42 × 0.75, both male
Optical path length
Described as the minimum mechanically possible; no figure is given
Manual or motorised operation
A thread adapter — no optics, and not a filter wheel
Light sealing
Aluminium, anodised black with a matt internal wall
Power
Not published by the maker.
Software support
Not published by the maker.
Amazon reference
B0C7BYJ588 (same reference on 5 Amazon marketplaces)
EAN
4895243557307
  • The matt internal finish addresses internal reflections, which few adapter listings mention
  • Both threads are named with their pitch
  • A double-male ring only helps where both sides are female — which is not every junction

Best for: Joining two female-threaded components of different sizes in an imaging train

≈ €10
Check price on Amazon

Specifications

Slot count and filter size
M48 × 0.75 and M42 × 0.75, both male
Optical path length
Described as the minimum mechanically possible; no figure is given
Manual or motorised operation
A thread adapter — no optics, and not a filter wheel
Light sealing
Aluminium, anodised black with a matt internal wall
Power
Not published by the maker.
Software support
Not published by the maker.
Amazon reference
B0C7BYJ588 (same reference on 5 Amazon marketplaces)
EAN
4895243557307

A double-male ring

M48 × 0.75 on one face, M42 × 0.75 on the other, both male. That joins two female-threaded components, which is a different problem from the one the step-up rings on this shelf solve — and it is worth checking which way round your own junction runs before ordering.

The internal finish

Anodised black outside, matt on the inner wall. Reflections inside an adapter near the focal plane show as reduced contrast or as a visible ring, and a blackened bore is a real manufacturing decision rather than a cosmetic one.

The uses the maker names

Screwing a focal reducer into the telescope side of a filter wheel, and fitting a 1.25 in filter to a 2 in eyepiece. The first is a genuine imaging junction; the second works mechanically and restricts the beam.

The number that never appears

Length. Described as minimal, never measured. In a back focus budget where a reducer demands one exact distance, “minimal” is not a number.

Availability

German, French, Italian and Spanish Amazon stores ran from 10 € to 15 € 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 filter wheels

  • NVZPG M48 to M28.5 filter adapter ring

    NVZPG AP M48 to M28.5 filter adapter

    A threaded ring that holds a 1.25 in filter in a 2 in filter drawer, converting M48 to M28.5.

    Slot count and filter size
    M48 to M28.5 — the 2 in filter thread to the 1.25 in filter thread
    Optical path length
    Not published by the maker.
    Manual or motorised operation
    A filter adapter ring — not a wheel and not a drawer
    Light sealing
    Not published by the maker.
    Power
    Not published by the maker.
    Software support
    Not published by the maker.
    Amazon reference
    B0FBL5WGD6 (same reference on 5 Amazon marketplaces)
    EAN
    9106667044416
    • Solves a real and common problem for a few euros
    • Both threads are named precisely rather than given as inch sizes alone
    • A 1.25 in filter in a 2 in path can vignette a large sensor

    Best for: An imaging train with a 2 in drawer and a collection of 1.25 in filters

    ≈ £35 / €42
    Check price on Amazon
  • Omegon low-profile M48 to T2 adapter ring

    Omegon M48 to T2 adapter, low profile (49749)

    A short adapter converting an M48 internal thread to a T2 external thread, with the maker emphasising that its low profile avoids focus problems.

    Slot count and filter size
    M48 female · T2 male — that is M42 × 0.75
    Optical path length
    Very low, as the maker states it; no figure is given
    Manual or motorised operation
    A thread adapter — no optics, and not a filter wheel
    Light sealing
    Not published by the maker.
    Power
    Not published by the maker.
    Software support
    Not published by the maker.
    Amazon reference
    B01KPR3X1K (same reference on 6 Amazon marketplaces)
    EAN
    4049467497493
    • The maker addresses back focus directly rather than leaving it to be discovered
    • A named list of what it is meant to connect, which most adapter listings omit
    • “Very low” is not a millimetre figure

    Best for: Bringing a 2 in filter thread onto a T2 camera fitting with minimal focus loss

    ≈ £19 / €19
    Check price on Amazon
  • ZGYDNM M54 filter drawer with two filter slides

    ZGYDNM M54 filter drawer with two slides

    A filter drawer rather than a wheel: two slides carry the filters, and the body threads M54 × 0.75 at both ends.

    Slot count and filter size
    M54 × 0.75 at the telescope end and M54 × 0.75 at the output · Two
    Optical path length
    4 mm is given for the interface and 16 mm as the extended length; both are reproduced as published
    Manual or motorised operation
    A filter drawer — the filters slide in and out, they do not rotate
    Light sealing
    Not published by the maker.
    Power
    Not published by the maker.
    Software support
    Not published by the maker.
    Amazon reference
    B0DK5TJY4G (same reference on 5 Amazon marketplaces)
    EAN
    9106666473491
    • A drawer consumes far less optical path than a wheel
    • Two slides mean a filter can be swapped in seconds without unthreading anything
    • The listing gives two different thickness figures without saying which is which

    Best for: A short back-focus imaging train where a wheel would not fit

    ≈ £61 / €72
    Check price on Amazon

The rest of this rack

  • 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
    Check price on Amazon
  • 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
    B07PRN86R5 (same reference on 5 Amazon marketplaces)
    EAN
    0736342781627
    • 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
    Check price on Amazon
  • SVBONY 0.5x focal reducer with C-mount adapter

    SVBONY 0.5x reducer with C-mount adapter (SV0.5x)

    A fully multi-coated 0.5x reducer for 1.25 in fittings, supplied with a C-mount adapter for cameras that use that thread.

    Reduction factor
    0.5x, from the title
    Required back focus
    Neither is published
    Image circle
    Not published by the maker.
    Corrector function
    Focal reducer with optics
    Thread standards
    1.25 in (3.2 cm), from the title
    Vignetting
    Not published by the maker.
    Housing
    Fully multi-coated, from the title
    Amazon reference
    B0792XJWFS (same reference on 1 Amazon marketplace)
    EAN
    0609378745560
    • The C-mount adapter suits the small cameras that C-mount threads are found on
    • Fully multi-coated is claimed, which is the strongest of the four coating labels
    • The listing has no description whatsoever beyond its title

    Best for: A small sensor camera with a C-mount thread on a long-focal-length telescope

    Check price on Amazon

All filter wheels