Skip to content

Extension tubes

Bresser Extension sleeve 37.5 mm for HEXAFOC (4940110)

An aluminium extension sleeve of 37.5 mm with M68 × 0.75 male and female threads, intended for the 2.5 in HEXAFOC focuser.

Bresser 37.5 mm M68 extension sleeve in aluminium

Bresser Extension sleeve 37.5 mm for HEXAFOC (4940110)

An aluminium extension sleeve of 37.5 mm with M68 × 0.75 male and female threads, intended for the 2.5 in HEXAFOC focuser.

Length
37.5 mm, from the title
Barrel and thread fittings
M68 × 0.75 internal and external, as the maker publishes them
Internal blackening
Matt black coated against stray light
Clamping method
Not published by the maker.
Rigidity
Not published by the maker.
Material
Aluminium
Amazon reference
B07PMKL9N3 (same reference on 5 Amazon marketplaces)
EAN
4007922060859
  • Both the length and the thread are published, which is everything an extension needs to state
  • M68 is the large-format thread that suits a 2.5 in focuser without narrowing the path
  • M68 × 0.75 is a specialist thread and will need adapters to meet T2 or M48

Best for: A Bresser HEXAFOC focuser that needs its focal plane moved further out

≈ €27
Check price on Amazon

Specifications

Length
37.5 mm, from the title
Barrel and thread fittings
M68 × 0.75 internal and external, as the maker publishes them
Internal blackening
Matt black coated against stray light
Clamping method
Not published by the maker.
Rigidity
Not published by the maker.
Material
Aluminium
Amazon reference
B07PMKL9N3 (same reference on 5 Amazon marketplaces)
EAN
4007922060859

Two figures and nothing missing

Thirty-seven and a half millimetres, M68 × 0.75 inside and out. For an extension sleeve that is the complete specification: how much path it adds and what it threads into.

Why a large thread

A 2.5 in focuser passes a wide cone of light. Putting an M48 component in that path would narrow it and darken the corners of a large sensor. M68 keeps the train matched to the focuser — at the cost of needing adapters to reach the more common threads.

The bore

Matt black inside. That is the minimum treatment for anything in the light path; the Omegon sleeve on this shelf uses ribbing, which scatters less still.

The listing’s repetition

Five bullets carrying three statements: two are repeated verbatim. Nothing is contradicted, and the specification that matters — length and thread — appears clearly.

Availability

German, French, Italian and Spanish Amazon stores ran from 27 € to 29 € on the day of the survey.

British Amazon catalogue holds a record for it that nobody is selling.

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 extension tubes

  • CHICIRIS 1.25 inch to 2 inch telescope eyepiece adapter

    CHICIRIS 1.25 in to 2 in adapter

    An adapter taking a 1.25 in eyepiece into a 2 in focuser, held by a brass compression ring rather than a bare thumbscrew.

    Length
    The listing gives none
    Barrel and thread fittings
    Holds a 1.25 in (31.7 mm) eyepiece in a 2 in (50.8 mm) focuser · Not mentioned
    Internal blackening
    Not published by the maker.
    Clamping method
    Brass compression ring, per the maker
    Rigidity
    Not published by the maker.
    Material
    Anodised aluminium
    Amazon reference
    B083587TGB (same reference on 5 Amazon marketplaces)
    EAN
    0738588852611
    • A brass compression ring protects the eyepiece barrel and keeps it centred
    • The conversion almost every 2 in focuser owner needs at some point
    • No length figure, and an adapter changes where the focal plane falls

    Best for: A 2 in focuser used with a collection of 1.25 in eyepieces

    ≈ €26
    Check price on Amazon
  • Omegon 2 inch extension sleeve with spring-ring clamp

    Omegon 2 in extension sleeve, 50 mm optical path (55072)

    A 2 in extension sleeve of 50 mm optical path with a spring-ring clamp, a filter thread at the lower end and internal ribbing against reflections.

    Length
    50 mm, as the maker publishes it
    Barrel and thread fittings
    2 in · 2 in, at the lower end
    Internal blackening
    Ribbed inside against reflections, black anodised outside
    Clamping method
    2 in spring-ring clamp, per the maker
    Rigidity
    Not published by the maker.
    Material
    Not published by the maker.
    Amazon reference
    B074FQH48F (same reference on 6 Amazon marketplaces)
    EAN
    4049467550723
    • Publishes the optical path added, which is the only figure that matters for an extension
    • A spring-ring clamp grips the barrel evenly instead of denting it with a screw
    • Fifty millimetres is a large step; finer adjustment needs a set of thin rings

    Best for: A telescope whose focal plane sits too far out for its eyepieces to reach

    ≈ £36 / €39
    Check price on Amazon
  • Explore Scientific set of five M48 extension sleeves

    Explore Scientific M48 extension sleeve set (0510381)

    Five threaded extension sleeves of 30, 20, 15, 10 and 5 mm, all M48 × 0.75, for fine adjustment of back focus in an imaging train.

    Length
    Not published by the maker.
    Barrel and thread fittings
    M48 × 0.75 on every sleeve
    Internal blackening
    Not published by the maker.
    Clamping method
    Not published by the maker.
    Rigidity
    Not published by the maker.
    Material
    Not published by the maker.
    Amazon reference
    B085HYZT9Y (same reference on 5 Amazon marketplaces)
    EAN
    4007922064154
    • Five published lengths that combine to any multiple of 5 mm up to 80
    • Threaded rather than push-fit, so nothing can tilt or slip in a long exposure
    • M48 only: a T2 train needs adapters at each end

    Best for: Dialling in the exact sensor spacing a reducer or flattener demands

    ≈ €55
    Check price on Amazon

The rest of this rack

  • ASToptics M54 male to T2 female adapter

    ASToptics M54 male to T2 female adapter (57801)

    A thread adapter from M54 male to T2 female, whose entire listing consists of generic statements about quality.

    Slot count and filter size
    M54 male, from the title · T2 female, from the title · Not stated for either thread
    Optical path length
    The listing gives none
    Manual or motorised operation
    A thread adapter — no optics, and not a filter wheel
    Light sealing
    Not stated
    Power
    Not published by the maker.
    Software support
    Not published by the maker.
    Amazon reference
    B0BPXFY2VT (same reference on 5 Amazon marketplaces)
    EAN
    4049467578017
    • M54 to T2 is a conversion the larger imaging trains genuinely need
    • From a maker whose range is sold through astronomy specialists
    • Five bullets and not one measurement, material or figure among them

    Best for: An M54 imaging train that has to meet a T2 camera fitting

    ≈ £36 / €39
    Check price on Amazon
  • 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
  • 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

All extension tubes