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Thread adapters

Briny River M42 to M48 step-up ring (390-EG)

A step-up ring converting the T-2 thread to M48, so that 2 in filters and M48 accessories can be fitted to T-2 components.

Briny River M42 to M48 anodised aluminium step-up ring

Briny River M42 to M48 step-up ring (390-EG)

A step-up ring converting the T-2 thread to M48, so that 2 in filters and M48 accessories can be fitted to T-2 components.

Slot count and filter size
M42 × 0.75 male — the T-2 thread · M48 × 0.75 female — the 2 in filter thread
Optical path length
The listing gives none
Manual or motorised operation
A thread adapter — no optics, and not a filter wheel
Light sealing
Aluminium alloy, anodised
Power
Not published by the maker.
Software support
Not published by the maker.
Amazon reference
DE B0FM49SGJH · US B0FM48JF46 · GB B0FM48JF46 · FR B0FM48JF46 · IT B0FM48JF46 · ES B0FM48JF46
EAN
4895264934644
  • Both threads are named precisely with pitch, which is what an adapter listing must do
  • Anodised aluminium resists the corrosion that ruins a thread left damp
  • No length figure, and every adapter consumes back focus

Best for: Putting an M48 filter or accessory onto a T-2 threaded component

≈ €9
Check price on Amazon

Specifications

Slot count and filter size
M42 × 0.75 male — the T-2 thread · M48 × 0.75 female — the 2 in filter thread
Optical path length
The listing gives none
Manual or motorised operation
A thread adapter — no optics, and not a filter wheel
Light sealing
Aluminium alloy, anodised
Power
Not published by the maker.
Software support
Not published by the maker.
Amazon reference
DE B0FM49SGJH · US B0FM48JF46 · GB B0FM48JF46 · FR B0FM48JF46 · IT B0FM48JF46 · ES B0FM48JF46
EAN
4895264934644

Two threads, both named properly

M42 × 0.75 male in, M48 × 0.75 female out. Naming the pitch alongside the diameter is what distinguishes a usable adapter listing from an ambiguous one — and it is also what distinguishes T-2 from the superficially similar M42 × 1.0 lens mount.

What it is for

T-2 is the thread most camera adapters and small accessories carry. M48 is the thread of 2 in filters and of larger imaging components. This ring bridges the two, in the direction that lets bigger accessories attach to smaller ones.

What it cannot do

Widen the light path. The M42 side remains the narrowest point, so a large sensor behind it will vignette regardless of the M48 accessory in front. Step-up rings solve mechanical problems, not optical ones.

The unpublished figure

Its length. Every part between telescope and sensor is subtracted from the back focus budget, and an adapter with no stated length has to be measured on arrival.

Availability

German, French, Italian and Spanish Amazon stores ran from 9 € to 14 € on the day of the survey.

American and British Amazon catalogues hold a record for it that nobody is selling.

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

  • 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
  • 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

The rest of this rack

  • Oumij1 0.5x focal reducer with M28.5 thread

    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
    Check price on Amazon
  • 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

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