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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.
Baader 6.5nm SII Filter - CMOS-Optimized

Baader 6.5nm SII Filter - CMOS-Optimized

by Baader Planetarium
SKU BAA-2961250
$176.00 - $468.00
$176.00
$176.00 - $468.00
$176.00
Price Match Policy!
  • 6.5nm FWHM Bandpass
  • Optimized for Modern CMOS Sensors
  • Suppresses Halos and Internal Reflections
  • High-Contrast for Sulfur-II Emission Nebulae
  • Available in Multiple Mounted and Unmounted Sizes
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  • Description
  • FAQ
  • Specifications
  • In the Box
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  • Baader 6.5nm SII Filter - CMOS-Optimized

    The Baader CMOS-Optimized SII Filter uses a tight 6.5nm bandpass to isolate the faint, deep-red light of ionized sulfur, a key structural component in bicolor and Hubble-palette astrophotography. This narrow window is specifically engineered to reject light pollution and moonlight, ensuring maximum signal-to-noise on emission nebulae when using modern, high-sensitivity CMOS sensors.

    High-Contrast SII Imaging with a 6.5nm Bandpass

    By restricting transmission to a narrow 6.5nm window centered on the Sulfur-II emission line, this filter renders the faint, intricate structures within nebulae like the Eagle Nebula (M16) and the Rosette Nebula (NGC 2237) with stark contrast. The tight bandpass darkens the sky background by rejecting unwanted artificial and natural light, allowing your sensor to record pure signal for cleaner, more detailed final images.

    CMOS-Optimized for Modern Sensors

    Legacy narrowband filters were not designed to handle the highly reflective nature of modern CMOS sensor packages. When paired with these sensors, older filters often produce distracting halos and internal reflections around bright stars. Baader's CMOS-optimized design incorporates advanced coating systems engineered to eliminate these artifacts at the source, saving you hours of complex post-processing.

    Advanced Coatings for Halo Suppression and Durability

    Each filter is planeoptically polished to ensure a sharp, distortion-free image and features advanced anti-reflection coatings. These coatings are not only essential for preventing halos but are also exceptionally hard and durable. This protects the filter from the effects of cleaning and exposure to the elements, ensuring consistent results for years of use.

    Available in 7 Sizes for Any Optical Train

    To accommodate nearly any imaging setup, the Baader 6.5nm SII filter is available in seven standard sizes. Whether you need a 1.25" or 2" mounted filter for a standard filter wheel, or an unmounted 31mm, 36mm, 50.4mm, 50x50mm, or 65x65mm filter for a dedicated camera or filter drawer, there is an option to fit your optical train perfectly.

  • What makes the Baader 6.5nm SII filter "CMOS-Optimized"?

    The "CMOS-Optimized" designation means the filter's anti-reflection coatings are specifically designed to suppress the halos and internal reflections that occur when using modern, highly reflective CMOS sensors. Legacy filters designed for older CCD technology often struggle with this, producing artifacts around bright stars that these Baader filters prevent.

    How does a 6.5nm bandpass on the Baader SII filter improve my images of the Eagle Nebula (M16)?

    The Eagle Nebula (M16) has strong Sulfur-II emissions that define the structure of its famous "Pillars of Creation." A tight 6.5nm bandpass isolates this specific light, rejecting light pollution and even strong moonlight. This dramatically increases the contrast of the pillars against the background sky, revealing finer details and structure that would be lost with a broader filter.

    Can I use the Baader CMOS-Optimized SII filter with my fast f/4 Newtonian telescope?

    Yes. A key part of the Baader CMOS-optimized design is ensuring the filter performs well with fast optical systems. The coatings and glass substrate are designed to minimize the bandpass shift that can occur with the steep light cones from fast telescopes, ensuring consistent performance even at focal ratios like f/4.

    Why should I choose the Baader 6.5nm SII filter over an older CCD-era filter?

    If you use a CMOS camera, the Baader 6.5nm SII filter is the superior choice. Older CCD filters lack the advanced anti-reflection coatings needed to prevent halos with reflective CMOS sensors. While a CCD filter may be less expensive, the Baader CMOS-Optimized filter will produce cleaner raw data, requiring significantly less effort in post-processing to remove artifacts.

    What is the benefit of imaging with a Baader SII filter for the Hubble Palette (SHO)?

    In the Hubble Palette, Sulfur-II (SII) data is typically mapped to the red channel. The Baader 6.5nm SII filter captures the unique structural details present in this emission line, which often differ from Hydrogen-alpha. This adds a critical layer of color differentiation and structural complexity to your final SHO composite image.

    How do I choose the right size Baader 6.5nm SII filter for my setup?

    The correct size depends on your camera sensor and filter holder.

    • 1.25" and 31mm: Best for smaller sensors (e.g., ASI1600, ASI294) to prevent vignetting.
    • 2" and 36mm: Ideal for APS-C sized sensors.
    • 50.4mm, 50x50mm, and 65x65mm: Required for full-frame and larger sensors to ensure the entire sensor is illuminated without vignetting.
    Always check your filter wheel or drawer specifications to confirm compatibility.
  • Bandpass (FWHM) 6.5nm
    Emission Line Sulfur-II (SII)
    Sensor Optimization CMOS
    Available Sizes 1.25" (Mounted), 2" (Mounted), 31mm (Unmounted), 36mm (Unmounted), 50.4mm (Unmounted), 50x50mm (Square), 65x65mm (Square)
    Net weight (kg) 0.01 (1.25" Round Mounted, 2" Round Mounted, 50.4mm Round Unmounted Filter)
    0.02 (50x50mm Square Filter)
    0.03 (65x65mm Square Filter)
    Filter shape round (1.25" Round Mounted, 2" Round Mounted, 31mm Round Unmounted Filter, 36mm Round Unmounted Filter, 50.4mm Round Unmounted Filter)
    square (50x50mm Square Filter, 65x65mm Square Filter)
    Single or Set? Single Filter
    Filter mounted Mounted (LPFC 6mm) (1.25" Round Mounted, 2" Round Mounted)
    Unmounted (31mm Round Unmounted Filter, 36mm Round Unmounted Filter, 50.4mm Round Unmounted Filter, 50x50mm Square Filter, 65x65mm Square Filter)
    Filter Usage CMOS, CCD, S-II
    Type of Filter Narrowband
    Special Features CMOS-optimized with Life-Coat™
    Filter Thickness (without cell) 2 mm (1.25" Round Mounted, 2" Round Mounted, 31mm Round Unmounted Filter, 36mm Round Unmounted Filter)
    3 mm (50.4mm Round Unmounted Filter, 50x50mm Square Filter, 65x65mm Square Filter)
    CWL (Central Wavelength) 671.7 nm
    AR-Coating Reflex-Blocker™ hard coated, planeoptically polished
    Suitable for f/ratio > f/3.4

    • Baader 6.5nm SII CMOS-Optimized Filter

      (Size as selected)

    • Filter Case

      (For individual filters)

  • Baader Planetarium Warranty