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Baader 6.5nm 36mm H-alpha Filter - CMOS-Optimized (OPEN BOX)
Baader 6.5nm 36mm H-alpha Filter - CMOS-Optimized (OPEN BOX)

Baader 6.5nm 36mm H-alpha Filter - CMOS-Optimized (OPEN BOX)

by Baader Planetarium
SKU BAA-2961100-36-OPENBOX
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  • Isolates the 656.3nm H-alpha emission line
  • 6.5nm bandpass for high-contrast imaging
  • 36mm unmounted format for filter wheels
  • CMOS-optimized to suppress reflections and halos
  • (OPEN BOX) Item: fully functional, may have cosmetic imperfections or non-original packaging
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  • Description
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  • Baader 6.5nm 36mm H-alpha Filter - CMOS-Optimized (OPEN BOX)

    This open-box Baader H-alpha Filter isolates the critical 656.3nm wavelength with a narrow 6.5nm bandpass, dramatically increasing contrast on emission nebulae. Designed for modern astronomy, the 36mm unmounted format integrates seamlessly into standard filter wheels, while its advanced coatings are optimized for the steep light cones of fast telescopes and the high sensitivity of CMOS sensors.

    A 6.5nm Bandpass for Maximum Nebula Contrast

    The filter's 6.5nm Full-Width Half-Maximum (FWHM) is engineered to isolate the hydrogen-alpha emission line from background light pollution and natural skyglow. This narrow window darkens the sky background significantly, making faint structures in objects like the North American Nebula (NGC 7000) or the Heart Nebula (IC 1805) stand out with striking clarity.

    CMOS-Optimized Coatings for Halos and Fast Optics

    Modern CMOS sensors are highly reflective, a common source of halos around bright stars. Baader's CMOS-optimized coatings are specifically designed to suppress these reflections. Additionally, the filter coatings are engineered to resist passband shift, ensuring the 6.5nm window stays centered on the H-alpha line even when used with fast optical systems down to f/4.

    The 36mm Unmounted Format for Filter Wheels

    The 36mm unmounted format is the standard for many popular astronomical filter wheels from manufacturers like ZWO and QHY. This size provides a generous clear aperture that prevents vignetting on sensors up to and including APS-C format, ensuring even illumination across the field for clean, flat frames.

    6.5nm H-alpha vs. Broader Bandpasses

    Compared to wider 12nm or 35nm H-alpha filters, a 6.5nm bandpass offers a significant advantage in light-polluted skies. While a wider filter might gather signal slightly faster, the trade-off is a brighter background that can wash out faint details.

    • 6.5nm Filter: Delivers the highest contrast, rejecting more unwanted light. It's the ideal choice for suburban imagers or for separating fine details in complex nebulae.
    • 12nm+ Filter: A better choice for very fast systems (below f/4) where passband shift can be more extreme, or for applications where maximizing signal in the shortest time is the primary goal.

    Critical Safety Warning: Why a 6.5nm Filter is Unsafe for Solar

    This is a deep-sky filter for imaging nebulae at night and must never be used for solar observation. Specialized solar filters have bandpasses under 0.1nm (1 Ångström) and include additional energy rejection elements. Using a 6.5nm filter for solar viewing, even with a camera, directs concentrated and harmful solar energy into your equipment and poses an extreme and immediate danger to your eyesight.

  • What does "CMOS-Optimized" mean for the Baader 6.5nm H-alpha filter?

    "CMOS-Optimized" means the filter has advanced anti-reflection coatings that prevent halos from forming around bright stars, a common issue with highly reflective CMOS sensors. It also ensures the filter's 6.5nm passband does not shift significantly off the H-alpha wavelength when used in fast telescopes (f/4 or faster), maintaining signal and contrast.

    How does a 6.5nm bandpass on this H-alpha filter affect my images of the Orion Nebula (M42)?

    The 6.5nm bandpass will produce extremely high-contrast images of the Orion Nebula (M42). It will darken the sky background, suppress star bloat, and reveal fine, filamentary details within the nebula's structure that are often lost with broader filters, especially from urban or suburban locations.

    Is the 36mm Baader H-alpha filter compatible with my ZWO filter wheel?

    Yes, the 36mm unmounted filter size is a standard format and is designed to be fully compatible with filter wheels from major manufacturers, including ZWO, QHY, and others that accept this size.

    Will I see halos around bright stars like Alnitak with this Baader 6.5nm filter?

    While no filter can completely eliminate all optical artifacts, the CMOS-optimized coatings on this Baader 6.5nm H-alpha filter are specifically designed to minimize reflections. This significantly reduces the size and intensity of halos around bright stars like Alnitak in the Horsehead Nebula region, resulting in cleaner images.

    Can I use this Baader 6.5nm H-alpha filter with my f/4 Newtonian for imaging the Pelican Nebula (IC 5070)?

    Absolutely. This filter is an excellent choice for an f/4 Newtonian. The CMOS-optimized design ensures that the 6.5nm passband remains effective even with the steep light cone of an f/4 system, allowing you to capture high-contrast images of emission targets like the Pelican Nebula (IC 5070).

    Why can't I use this Baader H-alpha filter for viewing the Sun?

    This is a deep-sky filter, not a solar filter. It lacks the necessary energy rejection layers to block the Sun's intense heat and harmful radiation (like UV and IR). Pointing this filter at the Sun would instantly destroy your camera sensor and cause permanent, severe eye damage. Safe solar observation requires specialized filters with bandpasses under 0.1nm.

    What does "Open Box" mean for this Baader 36mm filter?

    An "Open Box" item is a product that has been returned or used for demonstration. The filter is optically and functionally perfect, but the packaging may be opened or non-original, and there might be minor cosmetic marks on the non-optical surfaces. It offers the full imaging of a new filter at a reduced price.

  • Baader Planetarium Warranty Policy