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IMPORTANT: Our store is located in Canada. All orders that include products manufactured outside of Canada or USA will be subject to tariffs and duties, regardless of the order value. US customers are responsible for all applicable duties and tariffs, and those will be billed by the carrier, except for the Lacerta upgrade kit, for which we collect them at checkout.
Optolong H-alpha 3nm Narrowband Filter

Optolong H-alpha 3nm Narrowband Filter

by Optolong
SKU OPT-14103
$339.00 USD - $419.00 USD
$339.00 USD
$339.00 USD - $419.00 USD
$339.00 USD
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  • H-alpha 656.3nm Emission Line
  • 3nm FWHM Bandpass
  • Anti-Halo Design
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  • Description
  • Specifications
  • In the Box

  • Optolong H-Alpha 3nm Narrowband Filter

    The Optolong H-Alpha 3nm is a high-performance atmospheric suppression tool designed for high-resolution deep-sky imaging. By restricting the passband to a tight 3nm FWHM (Full Width at Half Maximum), this filter maximizes the signal-to-noise ratio (SNR) of the 656.3nm emission line while aggressively rejecting broadband interference from both artificial light pollution and natural airglow.

    The H-Alpha (Hα) Emission Line

    In the vacuum of space, ionized hydrogen atoms emit photons at specific energy levels. The most critical for astrophotography is the Hydrogen-alpha line at 656.3nm. This wavelength is the primary indicator of HII regions—massive clouds of ionized gas where star formation occurs.

    Because H-alpha light penetrates interstellar dust more effectively than shorter wavelengths, using a dedicated 3nm filter allows for the mapping of high-density structural filaments in emission nebulae that are typically obscured in broadband RGB imaging.

    Optolong SHO Filters Transmission Diagram

    3nm FWHM: Signal Isolation and Contrast

    The transition from a standard 7nm filter to a 3nm bandwidth provides a measurable increase in contrast by narrowing the "window" of permitted light:

    • Sky Background Suppression: The narrower window reduces the amount of background skyglow and moonlight reaching the sensor. This results in a significantly lower noise floor, allowing for longer sub-exposures and the detection of faint nebulosity.
    • Star Diameter Reduction: By cutting out the continuum light around the H-alpha peak, star bloat is minimized. This produces tighter stellar profiles, ensuring that bright stars do not overwhelm the fine details of the nebular gas.
    • Urban Imaging: The 3nm passband is narrow enough to allow for high-contrast imaging even in Bortle 8 or 9 environments, as it effectively isolates the target signal from the overlapping spectra of high-pressure sodium and mercury vapor lamps.

    Ion-Assisted Deposition (IAD) and Thermal Stability

    Optolong utilizes Ion-Assisted Deposition (IAD) to apply the interference coatings. This vacuum-deposition process results in a high-density coating that is superior to standard evaporated films.

    • Zero CWL Shift: Precision narrowband filters can suffer from a shift in the Central Wavelength (CWL) due to temperature fluctuations. IAD technology ensures the coating is mechanically stable, keeping the 3nm window locked on 656.3nm throughout extreme temperature drops.
    • Durability: The resulting surface is physically hardened, making the filter resistant to the delamination and aging effects caused by humidity and environmental exposure.

    Optical Design and Halo Mitigation

    A common failure in narrowband filters is the presence of internal reflections around bright stars. The Optolong 3nm series utilizes a non-cemented optical substrate. By manufacturing the filter from a single piece of high-quality optical glass rather than laminating multiple layers, the number of internal reflective surfaces is halved.

    When combined with precision anti-reflection (AR) coatings, this design ensures that the H-alpha signal is transmitted with >90% efficiency while maintaining an optical density of >OD4 in the out-of-band regions, virtually eliminating reflections and halos.

  • Central Wavelength (CWL) 656.3 nm
    FWHM (Bandwidth) 3 nm
    Peak Transmission >90%
    Blocking Range 300–1100 nm
    Optical Density (OD) >OD4
    Substrate Polished Optical Glass
    Surface Quality 60/40 (MIL-O-13830)
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