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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 3.5nm / 4nm Narrowband Filter Set - CMOS-Optimized H-alpha/O-III/S-II

Baader 3.5nm / 4nm Narrowband Filter Set - CMOS-Optimized H-alpha/O-III/S-II

by Baader Planetarium
SKU BAA-2961670
$929.00 - $1,982.00
$929.00
$929.00 - $1,982.00
$929.00
Price Match Policy!
  • 3-Filter Set: H-alpha (3.5nm), O-III (4nm), S-II (3.5nm)
  • Ultra-Narrow Bandpasses for Maximum Image Contrast
  • CMOS-Optimized to Eliminate Halos and Internal Reflections
  • Parfocal Design Ensures Focus is Maintained Between Filters
  • Available in 7 Formats, from 1.25" Mounted to 65x65mm Square
  • Life-Coat™ Hard Coatings for Enhanced Durability
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  • Description
  • FAQ
  • Specifications
  • In the Box
  • Downloads
  • Warranty

  • Baader 3.5nm / 4nm Narrowband Filter Set - CMOS-Optimized H-alpha/O-III/S-II

    The Baader 3.5nm / 4nm Narrowband Filter Set provides imagers with three advanced filters—a 3.5nm H-alpha, a 4nm O-III, and a 3.5nm S-II—for capturing extreme-contrast Hubble Palette (SHO) images. Available in 7 formats from 1.25" mounted to 65x65mm square, this set is specifically engineered with Reflex-Blocker™ coatings to suppress reflections and halos on modern CMOS sensors, even in fast optical systems.

    3.5nm & 4nm Bandpasses: CMOS-Optimized for Maximum Contrast

    This set pushes narrowband imaging to its practical limit with a 3.5nm bandpass for H-alpha and S-II, and a slightly wider 4nm for the dimmer O-III line. These ultra-narrow windows dramatically increase contrast by rejecting more unwanted light from urban skies, moonlight, and natural skyglow compared to wider 7nm or 12nm filters. The result is a darker background and enhanced definition in faint nebulosity.

    Baader's CMOS-optimized design is critical for modern cameras. These filters feature advanced dielectric coatings that are plane-parallel and hard-coated to prevent the internal reflections between the filter and sensor that cause halos around bright stars. This ensures clean, artifact-free data, especially with fast refractors or HyperStar systems.

    Parfocal Design Across All 7 Filter Sizes

    Engineered for efficiency, all filters in this Baader set are parfocal, eliminating the need to refocus when switching between H-alpha, O-III, and S-II. This saves critical imaging time and simplifies automated sequences with a filter wheel. This parfocal commitment holds true across all 7 available sizes, from standard 1.25" and 2" mounted filters to large-format unmounted options for flagship cameras.

    • Life-Coat™ Durability: Baader's hard-coating technology provides a scratch-resistant surface that can withstand careful cleaning and harsh observing environments, ensuring a lifetime of use.
    • Sealed Coating Edges: The coating material is sealed at the filter edge, preventing moisture intrusion and degradation over time, a common failure point in lesser filters.
    • Consistent Thickness: Each filter is polished to a high degree of plane-parallelism, preventing any image shift or distortion when placed in the optical path.

    A Critical Safety Warning for the 3.5nm H-alpha Filter

    It is imperative to understand that the 3.5nm H-alpha filter in this set is a deep-sky, nebular filter and is absolutely not safe for solar observation or imaging. Its 3.5nm (or 35 Ångström) bandpass is thousands of times wider than a dedicated solar H-alpha filter, which must have a bandpass under 1 Ångström to safely isolate the chromosphere.

    Attempting to view the Sun visually through this filter will cause immediate and permanent eye damage, including blindness. While photographic use on the Sun is theoretically possible with extreme caution and additional energy rejection filters, it is not the intended purpose of this product and is strongly discouraged.

  • What does "CMOS-Optimized" mean for the Baader 3.5nm/4nm filter set?

    "CMOS-Optimized" means the filters are designed to combat internal reflections that occur between the highly-reflective surfaces of modern CMOS sensors and the filter itself. Baader uses advanced Reflex-Blocker™ coatings that are plane-parallel to prevent these reflections from creating halos and other artifacts around bright stars, a problem often seen with older filters not designed for modern sensors.

    How does this 3.5nm/4nm Baader set compare to wider 7nm filters?

    The primary advantage is higher contrast. By cutting the bandpass in half (from 7nm to 3.5nm), the filters reject significantly more light pollution, moonlight, and natural airglow. This results in a darker sky background and makes faint nebulosity stand out more clearly. The trade-off is that exposures need to be longer to achieve the same signal level, but the resulting signal-to-noise ratio on emission nebulae is much higher.

    Are the filters in the Baader Narrowband Set parfocal?

    Yes, all filters in the Baader 3.5nm/4nm set are designed to be parfocal. This means you can switch between the H-alpha, O-III, and S-II filters in your filter wheel without having to adjust your focuser. This is a significant time-saver, especially for automated imaging runs.

    Will I need to refocus my Celestron EdgeHD 8" when switching between the H-alpha and O-III filters?

    No, you should not need to refocus. The Baader 3.5nm/4nm filters are parfocal, so once you achieve sharp focus with one filter (e.g., H-alpha), the O-III and S-II filters will be in the same focal plane. This holds true for any telescope system, including an 8" EdgeHD SCT.

    Can I use the 3.5nm H-alpha filter in this set to view solar prominences?

    Absolutely not. This is extremely dangerous and will cause permanent blindness. A deep-sky H-alpha filter has a bandpass of 3.5nm (35 Ångströms). A safe, dedicated solar H-alpha filter has a bandpass of less than 0.1nm (1 Ångström). This filter lets in thousands of times more energy and is not designed for solar use in any capacity.

    I'm imaging the Pelican Nebula (IC 5070) from a Bortle 7 zone. Will this filter set help?

    Yes, this set is ideal for that scenario. The ultra-narrow 3.5nm and 4nm bandpasses are extremely effective at isolating the specific wavelengths of light from the Pelican Nebula (IC 5070) while aggressively rejecting the broadband light pollution typical of a Bortle 7 zone. You will be able to capture high-contrast data that would be impossible with broadband or wider narrowband filters from that location.

  • Filter Type 3-Filter Narrowband Set (H-alpha, O-III, S-II)
    H-alpha Bandpass 3.5nm
    O-III Bandpass 4nm
    S-II Bandpass 3.5nm
    Design CMOS-Optimized, Parfocal
    Available Formats 1.25" Round Mounted, 2" Round Mounted, 31mm Round Unmounted, 36mm Round Unmounted, 50.4mm Round Unmounted, 50x50mm Square, 65x65mm Square
    Net weight (kg) 0.02 (1.25" Round Mounted)
    0.04 (2" Round Mounted, 50.4mm Round Unmounted Filter)
    0.01 (31mm Round Unmounted Filter, 36mm Round Unmounted Filter)
    0.06 (50x50mm Square Filter)
    0.10 (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? Filter-Set
    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, H-alpha, O-III, S-II
    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) 656.3 nm / 500.7 nm / 671.7 nm
    AR-Coating Reflex-Blocker™ hard coated, planeoptically polished
    Suitable for f/ratio > f/3.4
  • Baader Planetarium Warranty