New 3nm Ultra Narrowband Astronomy Filters from Optolong

This premium narrowband filter set includes SII (3nm), H-Alpha (3nm), and OIII (3nm) filters, designed for high-resolution astrophotography of emission nebulae using monochrome CCD and CMOS cameras.

Ultra-narrowband imaging allows productive astrophotography even under strong moonlight or severe light-polluted skies, making it possible to maximise imaging opportunities on every clear night.

Data captured through each filter can be combined into a full-colour final image. A common approach is the HOO palette, using H-alpha for the red channel and OIII for both green and blue channels. H-alpha data can also be blended into RGB images to significantly enhance contrast and fine structural detail while preserving a natural colour balance.

H-Alpha 3nm Filter: The most widely used narrowband filter for deep-sky imaging, passing a precise 3nm bandwidth centred at 656nm. This filter strongly suppresses artificial light sources such as mercury vapour and sodium street lighting, as well as natural skyglow caused by atmospheric oxygen emission. The result is exceptionally high contrast and the ability to reveal delicate nebular structures that are otherwise lost in broadband imaging.

OIII 3nm Filter: Designed for imaging emission nebulae at the 500nm oxygen-III emission line, allowing a 3nm bandwidth to pass. This filter effectively blocks artificial light pollution and unwanted atmospheric glow. OIII emission occurs at 495.9nm and 500.7nm, producing a characteristic blue-green colour. Many planetary nebulae and supernova remnants are imaged using only H-alpha and OIII filters, producing images with strong structure and naturally balanced colour similar to RGB data.

SII 3nm Filter: Optimised for imaging nebulae at the sulphur-II emission line centred at 672nm. With a narrow 3nm bandwidth, this filter efficiently blocks artificial light pollution and atmospheric skyglow, making it ideal for SHO (Hubble Palette) imaging where sulphur data adds depth and contrast to complex nebular regions.

IMPORTANT: Optolong filters are NOT designed for solar observation or solar photography. DO NOT use these filters to observe or photograph the Sun. Doing so will result in permanent eye damage.

Transmission Chart

SII Line: H-Alpha, 3nm centred at 656nm.

Green Line: SII, 3nm centred at 672nm.

Blue Line: OIII, 3nm centred at 500nm.

Technical Data

• Schott optical glass substrate
• Thickness: 2.0mm (36mm), 1.85mm (2")
• Surface Quality: 60/40 (MIL-O-13830 standard)
• Fine-optically polished to λ/4 wavefront accuracy
• <30 arc-second parallelism
• 85%+ transmission at passband
• Infrared cut-off from 700–1000nm
• High-precision off-band blocking

Coating Parameter

• Multi-layer anti-reflection coatings
• Non-cemented optical substrate coating
• Electron-beam evaporation with ion-assisted deposition for enhanced durability and scratch resistance
• Excellent central wavelength stability with minimal temperature-induced shift
• Planetary rotation coating system ensures uniform coating density and high optical performance

Filter Cell

• Ultra-thin filter cell minimises vignetting while maximising clear aperture
• Clear aperture: 26mm (1.25"), 45mm (2")
• Aerometal construction with precision CNC machining
• Sand-blasted, black-anodised finish with internal anti-reflection treatment
• Laser-engraved markings for permanent identification

Sample Images

NGC7000 © Tommaso Massimo Stella

NGC6960 © Andrea Andreotto Maggi Astrophoto

H-Alpha 3nm Test © YaGe