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Focal reducers

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.

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

Specifications

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 same product, described identically

Five bullets, word for word the same as another 0.5x reducer on this shelf. Same thread, same factor, same housing, same exclusions. Different manufacturer references, different sellers, different prices by market.

Why that is worth saying

Because a reader comparing two listings might reasonably assume two different products with two different sets of properties. On the published information there is nothing to choose between them, and this page says so rather than manufacturing a distinction.

What the thread tells you

M28.5 × 0.6 is the filter thread of every 1.25 in eyepiece. Naming it correctly — as both these listings do — means the reducer will engage the eyepiece nose without an adapter.

The limits

Very fast telescopes and wide-angle eyepieces, both excluded by the maker. Clear aperture and spacing, both unpublished. What remains is a cheap, simple way to widen the field of a long instrument.

Availability

French, Italian and Spanish Amazon stores ran from 21 € to 25 € on the day of the survey.

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

American and British 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.

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

  • 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

The rest of this rack

  • 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
    B018TN4TCO (same reference on 6 Amazon marketplaces)
    EAN
    4049467474043
    • The transmission is published as a percentage rather than a word
    • Neutral rather than tinted, so lunar colour is not altered
    • A single fixed value suits one range of phases and apertures

    Best for: A wide-field 2 in eyepiece used on the Moon at first or last quarter

    ≈ €39
    Check price on Amazon
  • Vixen 1.25 inch moon filter

    Vixen Moon filter 1.25 in (37222-5)

    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
    High-quality plane-parallel glass, as the maker states it
    Cell depth
    Not published by the maker.
    Amazon reference
    B0018HILMI (same reference on 6 Amazon marketplaces)
    EAN
    4955295372225
    • Plane-parallel glass is the property that keeps the image sharp at high magnification
    • A 1.25 in thread fits the eyepiece size almost everyone owns
    • No transmission percentage, so it cannot be compared with the filters beside it

    Best for: A 1.25 in eyepiece case where substrate quality matters more than a published figure

    ≈ $54 / £42 / €45
    Check price on Amazon
  • Diealles Shine black telescoping folding stool

    Diealles Shine Telescoping folding stool

    A polypropylene telescoping stool with a carry strap, described in five bullets that contain no measurement at all.

    Seat height range
    The listing gives none
    Adjustment method
    Not published by the maker.
    Steps
    The listing gives none
    Load rating
    The listing gives none — described as a large capacity
    Folded size
    The listing gives none
    Weight
    The listing gives none
    Foot design
    Not published by the maker.
    Seat material
    Polypropylene, described as an upgraded version
    Supplied accessories
    Supplied straps for hand or shoulder
    Amazon reference
    B0BWF25TX6 (same reference on 5 Amazon marketplaces)
    EAN
    0788135722737
    • The same telescoping principle as its better-documented rivals
    • Carry straps are supplied rather than sold separately
    • Not one measurement appears anywhere in the listing

    Best for: Nobody who has not seen one in person or measured what they need

    ≈ €20
    Check price on Amazon

All focal reducers