Svbony SV231 Color Correction Filter 1.25″ review

The Svbony company continues to delight astronomy lovers with a variety of accessories. I received an interesting filter for testing to  chromatism suppression – Svbony SV231 Color Correction Filter 1.25″.

Svbony SV231
Svbony SV231

Chromatism in an achromatic lens telescope is a aberration that appears as a blue or purple halo around bright objects (planets, moon, stars). Chromatism appears due to the inability of an achromatic telescope to bring all rays in the visible range into focus – usually only red and green rays are brought together. This is especially actual for fast (f5-f6) achromats. Some people, unknowingly, even consider these halos to be the “atmosphere” of stars or planets. In ED telescopes and apochromats, chromatism can be significantly reduced or even completely eliminated compared to conventional achromatic telescopes. However, the cost of ED refractors and apochromats is significantly higher than that of achromats. I would also like to add that people’s tolerance for chromaticism may vary. Some people don’t see chromatism at all, for others it doesn’t bother them, and for others it irritates them. In my opinion, an age factor may also play a role here, since with age the lens in the eye turns yellow and acts as a kind of light filter. Moreover, a person can get used to the yellow image, and thus not notice the chromatism. My left eye is a little yellowish. But children and teenagers are great at noticing chromatic halos thanks to the young transparent lens.

Characteristics declared by the manufacturer:

Model SV231
Filter Usage Color Correction Filter
Type of Filter Bandpass
Size 1.25″
Substrate Thickness 1mm
Clear Aperture 26mm
Wavelength Range 300-1200nm
Blocking >OD2
Peak transmittance >95%
Surface Quality 60/40
Surface parallelism 1/2λ
Thread M28.5×0.6
Single Thread Yes
Net Weight 4.2g /0.15oz

Bandwidth (manufacturer’s schedule):

Claimed to block infrared and ultraviolet radiation.

Having opened the parcel, I found a cardboard box, inside of which, in a small plastic bag, there was a large plastic box with a light filter.

Фильтр в коробке
Filter in the box
Фильтр в коробке
Filter in the box

A few measurements
Filter frame diameter: 31.77mm
Thickness (with thread) 6.96 mm
Thickness (without thread) 5.6 mm
There are external (28.30 mm) and internal (27.81 mm) threads.

When held up to the light, the filter looks yellowish; when the filter is tilted, the color changes. The glare from the surfaces is purple.

Слева - IR-cut, справа - Svbony SV231.
Left – IR-cut, right – Svbony SV231.

Sunlight spectroscope test:

Svbony SV231 - спектр
Svbony SV231 – spectrum

By the spectrum, Svbony SV231 really cuts off infrared and ultraviolet radiation, as well as the violet part of the spectrum.

During visual observations through the Svbony SV501P achromat, a 70 mm light filter significantly, but not completely, reduces the chromatic halo. In this case, the image acquires a yellowish tint. There is no point in using this filter with telescopes without chromatism.

Approximate view of the Sun through the Svbony SV501P 70 mm achromatic telescope with a Herschel wedge and ND3.0 filter.
On the left is an additionally installed IR-cut light filter, on the right is a Svbony SV231 light filter.

IR-cut vs Svbony SV231
IR-cut vs Svbony SV231

Another example of images with an IR-cut filter (top) and Svbony SV231 (bottom) through a telescope Svbony SV501P 70 mm.

The Svbony SV231 Color Correction Filter 1.25″ is suitable for reducing chromatism in achromatic refractors in both visual and photographic modes. It does not completely eliminate chromatism, but it does not color the image too much, like denser yellow filters. Adds new details to the image it will not add, but the chromatism will be less noticeable. Also, the Svbony SV231 light filter is suitable for ground-based observations.
You can buy the Svbony SV231 Color Correction Filter 1.25″ on aliexpress here.

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