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ZWO Narrowband SII Filter - 7nm
ZWO Narrowband SII Filter - 7nm
ZWO Narrowband SII Filter - 7nm
ZWO Narrowband SII Filter - 7nm
ZWO Narrowband SII Filter - 7nm
ZWO Narrowband SII Filter - 7nm
ZWO Narrowband SII Filter - 7nm
ZWO Narrowband SII Filter - 7nm

ZWO Narrowband SII Filter - 7nm

by ZWO
SKU ZWO-SII7nm1.25
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  • Isolates the 672nm Sulfur-II emission line
  • 7nm bandpass for high-contrast imaging
  • 1.25" or 2" threaded cell, or 36mm unmounted
  • 1/4 wave polished on both surfaces
Size
2 in stock
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  • Description
  • FAQ
  • Specifications
  • In the Box
  • Downloads
  • Warranty

  • ZWO SII 7nm Narrowband Filter

    The ZWO SII 7nm Filter isolates the deep-red Sulfur-II emission line centered at 672nm, a critical wavelength for mapping ionized structure in emission nebulae. Its tight 7nm bandpass dramatically increases contrast by rejecting light pollution and moonlight, while the 1/4 wave polished substrate ensures that the finest details are not lost to optical imperfections.

    Isolating Deep-Red Structure with a 7nm Bandpass

    By restricting transmission to a narrow 7nm window around the 672nm SII line, this filter renders the sky background nearly black, causing faint nebulosity to stand out with striking clarity. This high signal-to-noise ratio is essential for revealing the delicate, wispy structures in supernova remnants like the Veil Nebula (NGC 6960) or the intricate star-forming regions within the Eagle Nebula (M16).

    1/4 Wave Optics for High-Fidelity Imaging

    Each ZWO narrowband filter is ground and polished to a 1/4 wave surface accuracy, a specification that prevents distortion and maintains image sharpness across the field. It transmits about 90% at the 672nm SII line, blocks off-band light to below 0.1% (OD3) and cuts infrared from 700 to 1100nm, preserving the critical signal from your target.

    Building the Hubble Palette with the ZWO SII Filter

    This filter is the essential "S" component in the SHO color palette, made famous by images from the Hubble Space Telescope. When you combine data captured through this SII filter with separate exposures using Hydrogen-alpha and Oxygen-III filters, you can create stunning, scientifically valuable images that map the chemical composition of nebulae in vibrant gold, cyan, and blue hues. The 1.25" and 2" versions come in threaded cells for filter wheels and nosepieces, while the 36mm version is unmounted for filter wheels with 36mm unmounted slots.

  • What is the primary purpose of the ZWO 7nm SII filter?

    The ZWO 7nm SII filter is a narrowband filter designed for astrophotography with monochrome cameras. It isolates the 672nm wavelength of light emitted by ionized sulfur, which is crucial for capturing specific structural details in emission nebulae and creating "Hubble Palette" (SHO) images.

    Can I use the ZWO 7nm SII filter with a color camera?

    While technically possible, it is not recommended. Color cameras have a Bayer matrix (RGB filters) over their sensors, and only the red pixels will receive signal from the 672nm SII line. This results in a significant loss of signal and resolution, making a monochrome camera the superior choice for narrowband imaging.

    How does the ZWO 7nm SII filter perform on the Rosette Nebula (NGC 2237) with a monochrome camera?

    On a target like the Rosette Nebula, the ZWO 7nm SII filter excels at revealing the shock fronts and ionization structures that are less prominent in Hydrogen-alpha. It isolates the outer shell and filamentary details, providing the essential "S" channel data that adds depth and a golden hue to a final SHO composite image.

    What exposure times should I expect for the ZWO 7nm SII filter with an 8" f/4 Newtonian?

    With a fast f/4 system, you can typically start with exposures of 300 to 600 seconds per sub-frame from a moderately light-polluted (Bortle 4-5) site. Sulfur-II is often the faintest of the three main narrowband channels (Ha, OIII, SII), so you may need to expose 1.5x to 2x longer for SII than you do for Hydrogen-alpha to achieve a comparable signal level.

    Why is a 7nm bandpass important for the ZWO SII filter?

    A narrower bandpass is more effective at rejecting unwanted light, such as from city glow, moonlight, and natural skyglow. The 7nm bandpass provides a very high-contrast view by darkening the sky background significantly, making it superior to wider 12nm or 15nm filters, especially from suburban locations.

    Will the ZWO 7nm SII filter thread into a standard 1.25" filter wheel?

    Yes, the 1.25" version. It is mounted in a 1.25" metal cell with M28.5x0.6 male threads and fits any 1.25" filter wheel, filter drawer, or accessory that accepts standard 1.25" threaded filters. The 2" version uses M48x0.75 male threads, and the 36mm version is unmounted.

  • SKU ZWO-SII7NM1.25
    Filter Type Sulfur-II (SII) Narrowband
    Bandwidth 7 nm
    Size 1.25" mounted, 2" mounted, 36mm unmounted
    Mount Style Threaded cell (1.25", 2"); unmounted (36mm)
    Shape Round
    Category Single Filter
    Central wavelength 672 nm
    Cell thread 1.25": M28.5x0.6 male; 2": M48x0.75 male
    Cell height 1.25": 5.5 mm + 2.5 mm thread; 2": 5 mm + 2.5 mm thread
    Peak transmission About 90%

    • Sulfur II 7nm Filter (1.25", 2" or 36mm, as selected)

      × 1

    • Protective Plastic Case

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  • ZWO 2-Year Limited Warranty