SVBONY SV115 1.25″ OIII 18nm Narrowband Filter

Product Overview

The SVBONY SV115 1.25″ (item F9186A) is an O-III narrowband filter with an 18 ± 2 nm passband. It transmits 90% at the 495.9 nm and 500.7 nm doubly-ionized oxygen lines and blocks across 400–700 nm, using dichroic interference and anti-reflection coatings on 1.85 mm glass. It threads into any 1.25″ eyepiece or diagonal.

Who It's For

This is a good match if you observe emission and planetary nebulae visually and want more contrast between the nebula and the sky background, including on bright targets such as M42 from light-polluted locations.

Key Features & Design

• 18 ± 2 nm FWHM: centred on the O-III emission lines.
• 90% transmission at 495.9 nm and 500.7 nm.
• 400–700 nm blocking: suppresses the rest of the visible spectrum.
• Dichroic interference and anti-reflection coatings.
• 1.85 mm glass in a standard 1.25″ cell.

Optical Design

Planetary nebulae and many emission nebulae radiate strongly in the two O-III lines near 500 nm. By passing an 18 nm band around them and blocking the rest, the filter darkens the sky background far more than the nebula, so the object stands out. It increases contrast rather than brightness, which is why SVBONY recommends larger apertures under dark, clear skies with good seeing for the best results.

Recommended Uses

• Planetary nebulae such as the Ring and Dumbbell.
• Emission nebulae with strong O-III emission.
• Bright nebulae like M42 under light pollution.

Compatibility and Accessory Notes

• Size: 1.25″, threads into 1.25″ eyepieces and diagonals.
• 2″ version: SVBONY also makes the SV115 in 2″ as a separate product.

Good to Know Before You Order

• Contrast, not brightness: the filter dims stars and sky along with blocking light pollution; the nebula stands out because the background darkens more.
• Narrowband target list: it suits O-III-rich nebulae; galaxies and star clusters do not benefit.
• Weight: SVBONY does not publish a weight for this filter.

Frequently Asked Questions

Is it difficult to set up?

No. Thread it onto the bottom of a 1.25″ eyepiece or into a diagonal's nosepiece.

Will it remove light pollution?

It does not remove light pollution, but it increases the contrast between O-III nebulae and the sky.

Which telescope works best?

SVBONY recommends a large-aperture telescope under clear, dark skies with good seeing.

Bottom Line

In short: a 1.25″ 18 nm O-III filter with 90% line transmission and 400–700 nm blocking, for higher-contrast views of planetary and emission nebulae.