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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.
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 4nm Ultra-Narrowband OIII Filter - CMOS-Optimized

Baader 4nm Ultra-Narrowband OIII Filter - CMOS-Optimized

by Baader Planetarium
SKU BAA-2961400
$320.00 - $692.00
$320.00
$320.00 - $692.00
$320.00
Price Match Policy!
  • 4nm Ultra-Narrowband OIII Bandpass
  • Optimized for Modern CMOS Sensors
  • Reflex-Blocker™ Hard Coatings to Prevent Halos
  • Life-Coat™ Technology for Extreme Durability
  • Available in Multiple Mounted and Unmounted Sizes
1 in stock
Qualifies for FREE Shipping in CONUS on orders over $350.
  • Description
  • FAQ
  • Specifications
  • In the Box
  • Downloads
  • Warranty

  • Baader 4nm Ultra-Narrowband OIII Filter - CMOS-Optimized

    The Baader 4nm Ultra-Narrowband OIII Filter isolates the critical doubly-ionized oxygen emission line with a surgically precise 4nm bandpass, delivering maximum contrast for imaging emission nebulae. By aggressively blocking light pollution, moonlight, and extraneous starlight, this filter reveals the faintest filamentary details in targets like the Veil Nebula (NGC 6960) that are lost with wider filters.

    The 4nm OIII Bandpass Advantage for Maximum Contrast

    An ultra-narrow 4nm bandpass is an aggressive tool for astrophotography. It transmits only the light from ionized oxygen, dramatically darkening the sky background and increasing the signal-to-noise ratio on emission targets. This extreme selectivity makes the Baader 4nm OIII filter exceptionally effective even under moonlit or heavily light-polluted skies, turning compromised nights into productive imaging sessions.

    Reflex-Blocker Coatings for Halo-Free CMOS Imaging

    Modern CMOS sensors are notoriously reflective, often causing halos and internal reflections with traditional filters. Baader's CMOS-optimized filters directly address this with advanced Reflex-Blocker™ hard coatings. These coatings are meticulously designed to suppress reflections between the filter and the sensor, ensuring that bright stars like those in the Trapezium of the Orion Nebula (M42) remain sharp points of light, free from distracting artifacts.

    Life-Coat Durability and Plano-Parallel Optical Substrate

    Each Baader filter is built on a fine-optically polished, plano-parallel substrate, ensuring it will not degrade the resolution of your optical system. The dielectric coatings are applied with an Ion-Beam Assisted Deposition process, creating an incredibly hard, scratch-resistant surface. This Life-Coat™ technology means the filter can be cleaned repeatedly without fear of damage, guaranteeing its optical properties for a lifetime of use.

    Baader 4nm vs. 7nm OIII: When to Choose Ultra-Narrowband

    Choosing between a 4nm and a wider 7nm filter involves a direct trade-off between contrast and exposure time.

    • Wider (7nm) OIII Filter: Gathers light more quickly, allowing for shorter sub-exposures. It can be more forgiving of minor tracking errors and is often sufficient for dark-sky locations where light pollution is not the primary challenge.
    • Baader 4nm OIII Filter: Provides significantly higher contrast, which is essential for pulling faint details out from a bright sky background. While it requires longer exposure times, the resulting data is cleaner and reveals more intricate nebular structures, making it the superior choice for suburban imagers or anyone pursuing the highest possible detail.

  • What makes the Baader 4nm OIII filter "CMOS-Optimized"?

    The "CMOS-Optimized" design refers to Baader's proprietary Reflex-Blocker™ hard coatings. These coatings are specifically engineered to prevent halos and internal reflections that can occur between a modern, highly-reflective CMOS sensor and the filter surface. This results in cleaner images with sharper stars and fewer artifacts.

    How will the Baader 4nm OIII filter perform on the Veil Nebula (NGC 6960) with an f/5 Newtonian?

    The Baader 4nm OIII filter is ideal for targets like the Veil Nebula. Its extreme 4nm bandpass will produce outstanding contrast, separating the delicate, rope-like filaments of the nebula from the background sky. With an f/5 system, you will be able to capture deep data, but be prepared for longer sub-exposures compared to a wider filter to achieve a strong signal.

    Is the Baader 4nm OIII filter good for imaging planetary nebulae like the Ring Nebula (M57)?

    Yes, it is an excellent choice. Planetary nebulae are rich in OIII emissions. The 4nm bandpass will isolate the nebula's light, darken the sky background significantly, and help reveal faint structural details within the Ring Nebula (M57), such as its central star and subtle variations in the ring itself.

    Will I need longer exposures with the Baader 4nm OIII filter compared to a 7nm version?

    Yes. By restricting the bandpass to 4nm, the filter passes less light overall, including starlight. You should expect to roughly double your exposure time compared to a 7nm filter to achieve the same signal level. The benefit of this is a dramatic increase in contrast and rejection of unwanted light pollution.

    Does the Baader 4nm OIII filter cause halos around bright stars?

    No, this filter is specifically designed to prevent halos. The combination of the Reflex-Blocker™ coatings, non-aging sealed coating edges, and a high-quality plano-parallel substrate ensures that reflections are minimized, even on the brightest stars in the field of view.

    Is this Baader 4nm filter parfocal with other Baader CMOS-optimized filters?

    Yes. Baader manufactures their CMOS-optimized narrowband, LRGB, and high-speed filters to be parfocal. This means you can switch between filters in your filter wheel without needing to refocus, which is a critical time-saver for automated imaging sequences.

  • Bandpass 4nm
    Target Emission Line OIII (Doubly Ionized Oxygen)
    CMOS Optimized Yes, with Reflex-Blocker™ Coatings
    Available Sizes 1.25" Round Mounted, 2" Round Mounted, 31mm Round Unmounted, 36mm Round Unmounted, 50.4mm Round Unmounted, 50x50mm Square, 65x65mm Square
    Net weight (kg) 0.01 (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, O-III
    Type of Filter Ultra-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) 500.7 nm
    AR-Coating Reflex-Blocker™ hard coated, planeoptically polished
    Suitable for f/ratio > f/3.4
  • Baader Planetarium Warranty