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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 SII 6.5nm Narrowband Filter
Optolong SII 6.5nm Narrowband Filter
Optolong SII 6.5nm Narrowband Filter
Optolong SII 6.5nm Narrowband Filter
Optolong SII 6.5nm Narrowband Filter
Optolong SII 6.5nm Narrowband Filter
Optolong SII 6.5nm Narrowband Filter

Optolong SII 6.5nm Narrowband Filter

by Optolong
SKU OPT-11401
$159.00 - $229.00
$159.00
$159.00 - $229.00
$159.00
Price Match Policy!
  • Isolates the Sulfur-II (SII) emission line at 672nm
  • Tight 6.5nm bandpass for maximum contrast
  • Enables imaging in heavily light-polluted skies and during bright moonlight
  • Advanced ion-assisted multi-layer coatings for durability and stability
  • Available in 1.25" Mounted, 2" Mounted, and 36mm Unmounted sizes
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  • Description
  • FAQ
  • Specifications
  • In the Box
  • Warranty

  • Optolong SII 6.5nm Narrowband Filter

    The Optolong SII 6.5nm Narrowband Filter isolates a tight 6.5nm bandpass centered on the 672nm wavelength of doubly ionized sulfur. This precision allows imagers to capture the faint, structural details in emission nebulae, separating the specific SII signal from interfering light pollution and moonlight, which is critical when a 6.5nm window is all you have to work with.

    The 6.5nm Bandpass for Sulfur-II Emission

    This filter is engineered to transmit light from the specific 672nm emission line characteristic of ionized sulfur. The extremely narrow 6.5nm bandpass dramatically increases contrast by rejecting all other wavelengths, rendering the faint structures within nebulae against a dark sky background. This is essential for revealing details that are otherwise lost in the noise of broadband imaging.

    Imaging Through Moonlight and City Skyglow at 672nm

    By targeting only the 672nm SII line, the Optolong 6.5nm filter effectively blocks common sources of light pollution, including mercury vapor and sodium vapor streetlights. It also rejects natural skyglow from neutral oxygen emission, allowing you to continue imaging even under a full moon. This transforms weeks of potential downtime into productive imaging sessions, maximizing your time under the stars regardless of your location.

    The "S" in the Hubble Palette: Building Full-Color Narrowband Images

    The SII 6.5nm filter is a critical component of the "SHO" narrowband imaging trio, alongside Hydrogen-alpha and Oxygen-III filters. By assigning the data from each filter to a different color channel (Sulfur to Red, Hydrogen to Green, Oxygen to Blue), you can create the vibrant, high-contrast images famously associated with the Hubble Space Telescope. This technique reveals the chemical composition and structure of targets like the Pillars of Creation in the Eagle Nebula (M16).

    Ion-Assisted Coatings for 6.5nm Stability and Durability

    Optolong utilizes an advanced ion-assisted deposition coating process to ensure the filter's optical characteristics are precise and long-lasting. This technology produces a dense, scratch-resistant coating and guarantees the stability of the central wavelength (CWL). The 6.5nm bandpass will not deviate due to temperature changes during an imaging session, ensuring consistent, reliable data from dusk till dawn.

  • What is the primary use for the Optolong SII 6.5nm filter?

    The Optolong SII 6.5nm filter is designed for astrophotography of emission nebulae. It isolates the light emitted by ionized sulfur at a wavelength of 672nm, which dramatically increases the contrast of these objects, especially when used from light-polluted areas or as part of a multi-filter color composite image.

    How does the 6.5nm bandpass on the Optolong SII filter improve my images?

    A narrower bandpass like 6.5nm rejects more unwanted light from streetlights, moonlight, and natural skyglow compared to wider filters. This results in a darker sky background and higher contrast between your target nebula and the sky, allowing fainter details to be captured.

    Can I use the Optolong SII 6.5nm filter for visual observing?

    No, this filter is not recommended for visual use. The 6.5nm bandpass is so restrictive that it blocks nearly all visible light, making it impossible to see all but the very brightest nebulae. It is designed specifically for long-exposure imaging with sensitive astronomy cameras.

    How does the Optolong SII 6.5nm filter perform on the Rosette Nebula (NGC 2244) from a light-polluted location?

    The Rosette Nebula has significant Sulfur-II emission. Using the Optolong SII 6.5nm filter from a suburban or city location will allow you to capture the delicate filamentary structures within the nebula that would normally be completely washed out by skyglow. It is an essential tool for revealing the full structure of this and similar star-forming regions.

    What other filters do I need with the Optolong SII 6.5nm for full-color narrowband imaging?

    For full-color "Hubble Palette" (SHO) imaging, you will need two other narrowband filters:

    • Hydrogen-alpha (H-alpha) filter: Captures ionized hydrogen, typically the strongest signal.
    • Oxygen-III (OIII) filter: Captures ionized oxygen, which reveals high-energy regions.
    Combining data from these three filters allows you to create detailed and scientifically interesting false-color images.

    Will the Optolong SII 6.5nm filter work well with my fast f/4 Newtonian telescope?

    While narrowband filters perform optimally with slower focal ratios, Optolong's advanced coatings provide excellent stability. With very fast optical systems (f/4 and below), some narrowband filters can exhibit a slight shift in their central wavelength. However, the Optolong SII 6.5nm is widely used with fast telescopes and produces excellent results. For critical applications, ensure your imaging software can accommodate precise focus for each filter.

  • Filter Type Narrowband Interference Filter
    Bandpass 6.5nm
    Central Wavelength 672nm
    Primary Emission Line Sulfur-II (SII)
    Coating Technology Ion-Assisted Multi-layer Deposition
    Substrate Optical Glass
    Available Sizes 1.25" Mounted, 2" Mounted, 36mm Unmounted

    • Optolong SII 6.5nm Narrowband Filter (Selected Size)

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  • Optolong 3-Year Warranty