It multiplies the focal length, and the eye relief survives · review

SVBONY 0.5x reducer (EUF9115A) review

A 0.5x focal reducer in an anodised aluminium 1.25 in barrel, sold under the name “Barlow lens” while its own description correctly calls it a reducer.

By Jean-Benoit Buisson

The bottom line A useful, cheap reducer with a name that contradicts its function and a thread figure half a millimetre adrift.

The name is wrong and the description is right

The title calls this a Barlow lens. A Barlow multiplies focal length; this element halves it. The maker’s own bullets get it right — they describe a reducer that halves the main focal length and widens the field — which makes the title an error rather than a claim.

What a 0.5x element actually does

It shortens the effective focal length, which widens the true field and lowers the magnification of any eyepiece behind it. For imaging it also shortens the exposure needed for a given brightness, which the maker mentions.

The spacing caveat, published

The factor depends on the distance between the reducer and the focal plane. The maker states this outright, and it means the 0.5x on the label is the figure at one particular spacing rather than a fixed property.

The thread figure

The listing writes M28 × 0.6. The standard 1.25 in filter thread is M28.5 × 0.6. Half a millimetre of nominal diameter is the difference between a thread that engages and one that does not, and it is reported here as printed.

Availability

German, French, Italian and Spanish Amazon stores ran from 13 € 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 it publishes, and what it withholds

Strengths

The maker’s own description explains the effect correctly, including the spacing dependence
A 0.5x element widens the field on a telescope that cannot otherwise reach low power
Very inexpensive for the effect it produces

Compromises

It is sold under a name that means the opposite of what it does
The thread is written M28 × 0.6; the standard 1.25 in filter thread is M28.5 × 0.6
Reducers of this type vignette on larger sensors and at the field edge

Specifications

Amplification factor	0.5x, per the maker
Element count	Not published by the maker.
Barrel size	1.25 in, with the thread given by the maker as M28 × 0.6
Camera thread	Not published by the maker.
Effect on eye relief	The maker notes that the distance between reducer and eyepiece changes the factor
Coatings	Not published by the maker.
Body	Anodised aluminium
Weight	Not published by the maker.
Amazon reference	B078Z8ZYR8 (same reference on 5 Amazon marketplaces)
EAN	0601490337173

What observers ask about this one

Is it a Barlow or a reducer?

A reducer. A Barlow lens multiplies the telescope’s effective focal length — commonly 2x or 3x — and a 0.5x element divides it. The title uses the wrong word; the maker’s own bullets describe the correct behaviour.

Why does spacing change the factor?

Because a reducer’s effect depends on how far the focal plane sits behind it. The maker says so directly, which means the 0.5x figure applies at one particular spacing and drifts away from it at others.