ToupTek SHO Narrowband Filters

Narrowband filters are essential accessories in astrophotography used to isolate specific wavelength emission lines and enhance the signal-to-noise ratio of your target—especially for capturing breathtaking emission nebulae.

ToupTek SHO narrowband filters are precisely tuned to the three main ionized emission lines found in star-forming regions:

• Hα (656.3nm)
• SII (671.6nm)
• OIII (500.7nm)

By using these filters, you can effectively block urban light pollution and background stray light, dramatically enhance signal contrast, and bring out incredible detail—empowering you to achieve Hubble-like color mixing (SHO synthesis) in your astrophotography.

Technical Parameters

Size: 36mm (unframed) / 1.25” / 2”

Glass Thickness: 2mm

Transmission Range:

• H-alpha filter: Central wavelength 656.3nm
• SII filter: Central wavelength 671.6nm
• OIII filter: Central wavelength 500.7nm

Transmittance: >90%

FWHM:

• 36mm: H-alpha (4nm) / SII (4nm) / OIII (4nm)
• 1.25” & 2”: H-alpha (6.5nm) / SII (6.5nm) / OIII (6.5nm)

Glass Material: Quartz glass

Frame Material: Aluminum Alloy

Surface Treatment: Double-sided high-precision optical polishing

Coating Technology: IAD (Ion Assisted Deposition)

Coating System Design: AR anti-reflection coating + quartz glass + precision cutoff coating layer

OD: ≥5.0

Key Features

• Precise Band Control & Enhanced Detail Resolution
• The precise narrowband design effectively suppresses background noise while highlighting the emission structures of different elements, resulting in clearer celestial stratification and enhanced detail gradation.

• Hα filter: Central wavelength 656.3nm, FWHM 4nm.
• Optimized for hydrogen ionization regions, this filter serves as the primary channel for capturing nebular morphology.
• OIII filter: Central wavelength 500.7nm (OIII emission line), FWHM 4nm.
• Designed to reveal high-energy excitation zones, particularly effective for visualizing blue-green nebular details.
• SII filter: Central wavelength 671.6nm, FWHM 4nm.
• Enhances detection of faint signals and reveals structural stratification through ionized sulfur distribution. When combined with Hα, significantly improves image contrast.
• *FWHM for 1.25-inch and 2-inch filters is 6.5nm.
• High-Quality Quartz Glass, High Transparency and Purity
• The entire series of ToupTek Astro filters utilize high-quality colorless transparent quartz glass, with >90% high transmittance, high purity, exceptional blue-violet band transmission, and outstanding thermal stability—ideal for various demanding astronomical imaging applications.
• IAD Dense Coating, Durable and Stable
• Using IAD (Ion Assisted Deposition) coating technology, which is more costly than conventional vacuum evaporation but produces denser and more uniform coatings that are durable, corrosion-resistant, and have superior environmental stability.
• Precision Coating, Significantly Suppresses Halos
• ToupTek Astro filters employ a proprietary multi-layer system: a single-sided cutoff coating, front surface AR anti-reflection coating, and edge blackening treatment. This combination effectively minimizes internal reflections and stray light while ensuring coating integrity and extended service life.
• High Optical Cutoff Depth, Restores Natural Colors
• All channel filters have a cutoff depth of OD≥5.0, effectively blocking non-target spectral regions, avoiding band crosstalk and color cast, resulting in accurate and natural color reproduction.
• Matte Black Edge Coating, Easy Installation
• The filter edge is coated with a black matte treatment to minimize stray light, which ensures transmittance, reduces glare, and enhances image contrast.
• 36mm filters: The telescope-facing side has an inward-extending blackened border for quick orientation identification.
• 25″ & 2″ filters: Feature threaded aluminum alloy frames for direct screw-in installation, ensuring fast and tool-free mounting.
• Highly Compatible
• All filters use a single-piece, glue-free structure.
• 36mm: Recommended for APS-C and smaller cameras.
• 25″: Recommended for cameras with a 1-inch or smaller sensor.
• 2″: Recommended for full-frame and smaller cameras.
• Compatible with various brands on the market featuring 7-hole 36mm, 8-hole 1.25-inch, and 5-hole 2-inch electric filter wheels, offering a wider range of compatibility options.

Spectrum

Spectral Chart Reading Tips:

• The horizontal axis represents the wavelength of light (in nm), and the vertical axis represents light transmittance (percentage %).
• Red line: Hα (656nm); Green line: OIII (500.7nm); Blue line: SII (672.4nm).
• Emission nebula signal bands are mainly at 656nm (Hα), 500.7nm (OIII), and similar wavelengths.
• Light pollution peaks are often found near 540nm and 590nm (sodium/mercury lamp bands).

The transmission regions of our astronomical filters are engineered to avoid these interference bands, ensuring maximum signal clarity, enhanced contrast, and high image purity for deep-sky imaging.

ToupTek Astro HSO Narrowband Filter Performance

IC5070
Photographer: voice
Telescope: Sky-Watcher
Mount: UMI
Camera: ToupTek Astro ATR2600M
Filters: ToupTek Astro 36mm LRGB&SHO
Integration: Hα: 30 × 600s ; SII: 30 × 600s ; OIII: 30 × 600s
Total exposure: 15h

IC443
Photographer: voice
Telescope: Sky-Watcher F3.4
Camera: ToupTek Astro ATR2600M / ATR2600C
Mount: UMI
Filters: ToupTek Astro 36mm HSO
Processing: Narrowband combination using HSO channel mapping
Total exposure: 20h

NGC2237
Photographer: 原上行川
Telescope: Askar SQA55
Camera: ToupTek Astro ATR2600M
Mount: iOptron HAE16C
Filters: ToupTek Astro 36mm HSO
Astrophotography wireless controller: StellaVita
Integration: Hα: 71 ; OIII: 63 ; SII: 49
Total exposure: 15h

M16
Photographer: Yahushua
Telescope: Askar 130HNT28-AL
Camera: ToupTek Astro ATR585M
Mount: iOptron CEM26
Guide camera: G3M2210M
Filters: ToupTek Astro 1.25” HSO
Total exposure: 7h

NGC6357
Photographer: voice
Telescope: Sky-Watcher
Camera: ASI2600M
Filters: ToupTek Astro 2” HSO
Mount: UMi 17
Integration: Hα: 36 × 600s ; SII: 36 × 600s ; OIII: 36 × 600s
Total exposure: 18h

Installation

• 36mm unframed filters: Special coating eliminates ghosting. To install, align the side with the inward-extending black ring toward the telescope for instant orientation and improved convenience.
• 1.25″ & 2″ filters: Special coating removes front/back orientation concerns—simply screw in for fast, tool-free installation.