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Antlia 4.5nm Narrowband SII Edge Filter

Antlia 4.5nm Narrowband SII Edge Filter

by Antlia
SKU ANT-SII-4.5NM-1.25
CA$263.00 - CA$497.00
CA$263.00
CA$263.00 - CA$497.00
CA$263.00
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  • Captures ionized sulfur emissions at a central wavelength (CWL) of 672.4nm
  • Tight 4.5nm FWHM bandpass isolates faint nebulae from background skyglow
  • Peak transmission of over 90% at 672.4nm
  • Deep >OD5 out-of-band blocking from 300-1000nm suppresses unwanted light
  • Optimized for fast optical systems, usable down to f/3 with minimal signal loss
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  • Description
  • FAQ
  • Specifications
  • In the Box
  • Warranty

  • Antlia 4.5nm Narrowband SII Edge Filter

    The Antlia 4.5nm Narrowband SII Edge Filter isolates the critical 672.4nm emission line with a tight 4.5nm full width at half maximum (FWHM) bandpass and greater than 90% peak transmission. T>90% is guaranteed within 1nm range of the center bandwidth, and the filter delivers a superior signal-to-noise ratio and better contrast. It can be used with nearly all systems as fast as f/3 with minimal loss of signal, and its OD5 blocking covers the 300-1000nm range.

    4.5nm Bandpass with >90% Transmission at 672.4nm

    By restricting the bandpass to just 4.5nm, this filter improves contrast on deep-sky objects that contain SII emissions: SII emission nebulae, planetary nebulae, Wolf-Rayet nebulae and supernova remnants. With over 90% peak transmission at the 672.4nm line, it is designed to deliver high transmittance to reveal the faintest SII nebula structures.

    Engineered for Fast Optics: Usable Down to f/3

    A significant challenge with narrowband filters in fast optical systems (below f/4) is center-wavelength (CWL) shift, where the filter's bandpass moves away from the target emission line as the light cone becomes steeper. Antlia addresses this by guaranteeing T>90% within 1nm range of the center bandwidth. Antlia's blue-shift data shows the 4.5nm EDGE filters can be used with nearly all systems as fast as f/3 with minimal loss in emission signal, while conventional broader narrowband filters suffer a heavy loss in transmission from the CWL shift.

    OD5 Blocking and Lambda/4 Optics to Minimize Halos

    Image quality is defined by more than just transmission. The Antlia SII Edge filter is built on a single, non-glued optical substrate that eliminates internal reflections. Its coatings provide greater than OD5 blocking (suppressing 99.999% of unwanted light) from 300nm to 1000nm for a superior signal-to-noise ratio, and its steep spectral profile minimizes halos around bright stars.

    • Single Substrate: A single, non-glued substrate eliminates internal reflections.
    • Optical Specifications: Transmitted wavefront of Lambda/4 or better and parallelism of less than 30 arcseconds.
    • Edge-Blackened: All unmounted versions are edge blackened to eliminate internal reflections from stray light.

    Antlia 4.5nm Edge vs. Broader 7nm Filters: The Contrast Advantage

    Compared to filters with a 7nm or wider bandpass, the Antlia 4.5nm Edge passes less background light, so faint nebulae show higher contrast against the sky. This helps most from light-polluted locations or when the Moon is out, and the filter can be used in light-polluted areas and dark sites and extends imaging time when the moon is up. A narrower filter may need longer exposures to reach the same signal level.

  • How does the Antlia 4.5nm SII Edge filter perform on a fast astrograph like an f/4 Newtonian?

    The guaranteed T>90% within 1nm range of the center bandwidth keeps transmittance high when the center wavelength shifts in fast optics, and blue-shift data shows the filter can be used with nearly all systems as fast as f/3 with minimal loss of emission signal. An f/4 Newtonian is within that range.

    What kind of improvement will I see with the Antlia SII Edge filter on a target like the Soul Nebula (IC 1848)?

    The Soul Nebula is an emission nebula with SII emission. The 4.5nm bandpass at 672.4nm lowers the sky background and improves the contrast of its SII structures compared with broadband imaging, and the filter's steep spectral profile minimizes halos around bright stars.

    Why can't I use the Antlia 4.5nm SII filter for visual observation?

    Antlia does not recommend this filter for night visual observation. It is designed for imaging deep-sky objects that contain SII emissions.

    What does OD5 blocking mean for my astrophotos?

    OD5 blocking means the filter blocks over 99.999% of light outside its intended 4.5nm bandpass. This suppression of unwanted wavelengths (from 300-1000nm) gives a superior signal-to-noise ratio and better contrast.

    Is the Antlia 4.5nm SII Edge filter parfocal with other Antlia filters?

    The thickness is 2mm +/-0.05mm for the 1.25", 31mm, 36mm and 2" sizes and 3mm +/-0.05mm for the 50mm size. Parfocality is not specified for this filter, so check focus after changing filters, especially on very fast optical systems where the critical focus zone is small.

    Do I need to use this Antlia SII filter from a dark site?

    No. The filter can be used in light-polluted areas and dark sites, and it extends imaging time when the moon is up. The tight 4.5nm bandpass rejects much of the skyglow from city lights.

    WARNING: Can I use this filter for looking at the Sun?

    No. This is not a solar filter, and Antlia does not recommend it for solar imaging. DO NOT LOOK AT THE SUN WITH THIS FILTER. Serious eye damage will result if you fail to observe this warning.

  • Filter Type SII Narrowband (4.5nm EDGE series)
    Central Wavelength (CWL) 672.4nm
    Bandpass (FWHM) 4.5nm
    Peak Transmission >90%
    Transmission Guarantee T>90% within 1nm range of the center bandwidth
    Out-of-Band Blocking >OD5 (0.001%) @ 300-1000nm
    Recommended F-Ratio Usable down to f/3
    Substrate Optical, single / non-glued substrate
    Transmitted Wavefront Lambda/4 or better
    Parallelism < 30 arcseconds
    Surface Quality 60/40 (scratch/dig) per MIL-O-13830
    Filter Thickness 2mm ±0.05mm (1.25", 31mm, 36mm, 2")
    3mm ±0.05mm (50mm)
    Filter Cells (Mounted) 1.25" (M28.5x0.6), 2" (M48x0.75)
    Edge Treatment Unmounted filters are edge blackened
    Usage Warning Not recommended for solar imaging or night visual observation
    Warranty 3-years against delamination
    Filter Size 1.25" Mounted, 31mm Unmounted, 36mm Unmounted, 2" Mounted, 50mm Unmounted (by variant)

    • Antlia 4.5nm Narrowband SII Edge Filter (Selected Size)

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    • Protective Case

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  • 3-Year Manufacturer Warranty Against Delamination