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Focal reducers

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.

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

Specifications

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

A title and nothing else

The product name gives the factor, the fitting, the coating claim and the supplied adapter. Beyond that, this listing has no bullets and no description. Everything above comes from the name.

What a C-mount adapter tells you

That this is aimed at small sensor cameras. C-mount is a machine-vision and cine thread that many compact astronomy cameras carry, and supplying the adapter rather than assuming a 1.25 in nose is a sensible decision for that market.

The three figures a buyer needs

Clear aperture, element count and required spacing. The first decides whether a sensor is covered, the second how well the field is corrected, and the third where everything has to sit. None of them is published.

How to use it anyway

Start with the reducer as close to the sensor as the parts allow, take an exposure, and look at the corners. Stars stretching outwards mean the train is too long; inwards, too short. That is the empirical route when no figure is published.

Availability

No store in the survey held a live offer that day.

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

American, British, French, Italian and Spanish Amazon stores 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.

What this fits

More focal reducers

  • Astromania 0.5x focal reducer in black anodised housing

    Astromania 0.5x focal reducer (RC05X)

    A cemented two-element focal reducer of 85 mm focal length giving about 0.5x depending on spacing, with filter threads on both faces.

    Reduction factor
    About 0.5x, and the maker states it depends on the spacing
    Required back focus
    85 mm, as the maker publishes it
    Image circle
    22.5 mm, as the maker publishes it
    Corrector function
    Focal reducer with optics — two cemented elements
    Thread standards
    Filter thread on both faces; the maker writes it as 28.5 × 0.75 mm, where the convention on this shelf is M28.5 × 0.6
    Vignetting
    Not published by the maker.
    Housing
    Fully multi-coated, per the maker · Black anodised aluminium
    Amazon reference
    B01B2OR280 (same reference on 6 Amazon marketplaces)
    EAN
    6970019292991
    • Publishes its own focal length and clear aperture, which almost no reducer on this shelf does
    • States outright that the factor depends on spacing rather than printing 0.5x as fixed
    • The published thread pitch does not match the usual 1.25 in filter thread

    Best for: A long-focal-ratio telescope with a small sensor or a narrow-field eyepiece

    ≈ $18
    Check price on Amazon
  • EBTOOLS 2 inch to T2 telescope camera adapter

    EBTOOLS 2 in to T2 adapter

    A 2 in nosepiece adapter carrying a T2 male thread for the camera and an M48 internal thread for a filter, with a fully matted bore.

    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
    2 in nosepiece for a 2 in focuser · M42 × 0.75 male — the T2 thread · M48 × 0.75 internal, at the front
    Vignetting
    “Full frame with 2 inch, no dark corners”, as the maker states it
    Housing
    Fully matted internal thread; black hard-anodised outside
    Amazon reference
    B07MCH2CVN (same reference on 5 Amazon marketplaces)
    EAN
    0719527383403
    • Carries an M48 filter thread at the front, so a 2 in filter fits in the same part
    • Fully matted bore, which matters immediately in front of a sensor
    • The no-dark-corners claim is made without naming a sensor size

    Best for: Putting a T2-threaded camera into a 2 in focuser with a filter in the path

    ≈ £15 / €15
    Check price on Amazon
  • 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

The rest of this rack

  • Have A Seat telescoping stool in black with cushion

    Have A Seat HAS-001 telescoping stool

    An eleven-step telescoping stool reaching 45 cm with a 25 cm seat, a cushion and a bag, listed at 1.5 kg in its title and 1160 g in its bullets.

    Seat height range
    Eleven, reaching 45 cm
    Adjustment method
    A spring mechanism that engages each step, per the maker
    Steps
    Not published by the maker.
    Load rating
    Not given as a figure; described as carrying an average adult
    Folded size
    25 cm
    Weight
    The title says 1.5 kg; the fourth bullet says 1160 g. Both are reproduced here
    Foot design
    Not published by the maker.
    Seat material
    Described by the maker as patented
    Supplied accessories
    Seat cushion, bag and carry handle
    Amazon reference
    B09QMNJ4TW (same reference on 5 Amazon marketplaces)
    EAN
    4170000029076
    • Eleven steps to 45 cm covers the range a telescope actually needs
    • A spring mechanism that clicks into each step is quicker than a twist lock
    • The listing gives two different weights for the same stool

    Best for: An observer who wants a quick spring lock rather than a twist mechanism

    ≈ €35
    Check price on Amazon
  • Hesanzol portable telescoping stool with carry strap

    Hesanzol Portable telescoping stool

    A nylon and PA66 telescoping stool adjusting from 6.3 to 45 cm, rated to 180 kg, at a published 1.1 kg with a 25.9 cm seat.

    Seat height range
    6.3 cm to 45 cm, as the maker publishes it
    Adjustment method
    Two buckles, top and bottom, twisted to open and close
    Steps
    Not published by the maker.
    Load rating
    Up to 180 kg, as the maker states it
    Folded size
    25.9 cm, as the maker publishes it
    Weight
    1.1 kg, as the maker publishes it
    Foot design
    Non-slip underside
    Seat material
    High-strength nylon and PA66
    Supplied accessories
    Adjustable nylon strap and a storage bag
    Amazon reference
    B086ZJSTJX (same reference on 6 Amazon marketplaces)
    EAN
    0053552379766
    • The lightest stool on this shelf at a published 1.1 kg
    • Names its materials specifically rather than saying “plastic”
    • A 180 kg rating is lower than the 200 kg of two rivals here

    Best for: Carrying to a dark site on foot, where every hundred grams is counted

    ≈ $24 / £17 / €26
    Check price on Amazon
  • Semptec telescoping stool with carry strap

    Semptec Urban Survival Technology ZX8711 telescoping stool

    A ten-step telescoping stool rated to 200 kg at a published 982 g, with polypropylene body, polyester strap and a steel tension spring.

    Seat height range
    Ten, as the maker states them
    Adjustment method
    Not published by the maker.
    Steps
    Not published by the maker.
    Load rating
    Up to 200 kg, as the maker states it
    Folded size
    44 × 25 × 25 cm, as the maker publishes them
    Weight
    982 g, as the maker publishes it
    Foot design
    Not published by the maker.
    Seat material
    Polypropylene stool, polyester strap, steel tension spring
    Supplied accessories
    Carry strap · German instructions
    Amazon reference
    B0D9KLZSQZ (same reference on 6 Amazon marketplaces)
    EAN
    4022107434447
    • Under a kilogram, and the figure is published to the gram
    • A 200 kg rating with named materials including a steel spring
    • Ten steps is the coarsest adjustment of the telescoping stools here

    Best for: The best weight-to-rating ratio on this shelf

    ≈ €15
    Check price on Amazon

All focal reducers

Any figure written into the body of this page was true on the day it was written. The amount shown next to each instrument is requested from the retailer as the page loads, and it is that amount, not the text, that stands.