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Antlia 3nm Narrowband SII Pro Filter

Antlia 3nm Narrowband SII Pro Filter

by Antlia
SKU ANT-SII-3NM-1.25
CA$362.00 - CA$696.00
CA$362.00
CA$362.00 - CA$696.00
CA$362.00
Price Match Policy!
  • Isolates the Sulfur-II emission line at 672.4nm
  • 3nm bandpass (FWHM) to enhance contrast of emission targets
  • Peak transmission greater than 88%
  • Usable down to f/3 with minimal loss of signal
  • Out-of-band blocking rated at >OD5 (0.001%) from 300-1000nm
Size
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  • Description
  • FAQ
  • Specifications
  • In the Box
  • Warranty

  • Antlia 3nm Narrowband SII Pro Filter

    The Antlia 3nm Narrowband SII Pro Filter passes the 672.4nm sulfur-II line through a 3nm bandpass, which enhances the contrast of emission targets by lowering the unwanted background signal. Peak transmission is above 88% and out-of-band blocking is >OD5 across 300-1000nm. T>88% is guaranteed within 1nm of the center bandwidth, and the filter can be used down to f/3 with minimal loss of signal.

    A 3nm Bandpass at 672.4nm

    The core of the Antlia 3nm Pro series is its ultra-narrow 3nm full width at half maximum (FWHM) bandpass. It passes a narrow band around the 672.4nm line of ionized sulfur; as the bandwidth becomes narrower, less unwanted background signal gets through.

    Targets include SII emission nebulae, planetary nebulae, Wolf-Rayet nebulae and supernova remnants; the filter is only effective on deep-sky objects that contain SII emission, can be used in light-polluted areas and at dark sites, and extends imaging time when the moon is up.

    >88% Transmission Down to f/3

    Narrowband filters used with fast focal ratio telescopes can suffer from "blue shift," where the passband shifts away from the target emission line, causing significant signal loss. Conventional broader narrowband filters lose a lot of transmission from this CWL shift.

    Transmission is guaranteed at over 88% within a 1nm range of the 672.4nm central wavelength. Blue-shift data shows the 3nm Pro filters can be used with nearly all systems as fast as f/3 with minimal loss in emission signal.

    >OD5 Blocking from 300-1000nm

    Out-of-band blocking is rated >OD5: no more than 0.001% of light outside the bandpass gets through between 300nm and 1000nm.

    This delivers an excellent signal-to-noise ratio and an effective cut-off that minimizes interference from other wavelengths, and its optical reliability reduces post-processing.

    Lambda/4 Wavefront on a Single Substrate

    Each filter is built on a single, non-glued optical substrate, which eliminates internal reflections. Its steep spectral profile minimizes halos around bright stars.

    • Transmitted Wavefront: Lambda/4 or better.
    • Parallelism: Less than 30 arcseconds.
    • Edge Blackening: Unmounted filters have blackened edges, which eliminates internal reflections from stray light.
    • Surface Quality: Each filter meets a 60/40 scratch/dig surface quality standard per MIL-O-13830.

    Antlia 3nm Pro vs. Wider Filters: A Contrast Trade-Off

    A 3nm band passes less skyglow and moonlight around the SII line than a 5nm or 7nm band, so the background is darker.

    The emission line itself is far narrower than 3nm, so it passes either way; what changes is the background that comes with it. Broader filters also lose more transmission from the CWL shift on fast optics.

  • What is the main advantage of the Antlia 3nm SII Pro filter over a wider 5nm or 7nm filter?

    Higher contrast. The 3nm bandpass lets through less moonlight and light pollution around the SII line, so the background is darker.

    Can I use the Antlia 3nm SII Pro filter with my fast f/4 astrograph?

    Yes. f/4 is slower than the f/3 limit. The filter is guaranteed at T>88% within 1nm of the center bandwidth, and blue-shift data shows the filter can be used with nearly all systems as fast as f/3 with minimal loss in emission signal.

    How does the Antlia 3nm SII Pro filter perform on supernova remnants like the Veil Nebula (NGC 6960)?

    The Veil Nebula is a classic supernova remnant with distinct structures emitting in SII, H-alpha, and OIII. The SII filter records the sulfur emission at 672.4nm as its own channel for an SII/Ha/OIII composite. Supernova remnants are among its listed targets.

    Why is the >OD5 blocking on the Antlia 3nm SII Pro filter important?

    OD5 (Optical Density 5) means the filter blocks at least 99.999% of all unwanted light from 300nm to 1000nm. This delivers an excellent signal-to-noise ratio and minimizes interference from other wavelengths.

    Is the Antlia 3nm SII Pro 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. The 3nm Pro series is not specified as parfocal. Check focus after changing filters.

    Can I use the Antlia 3nm SII Pro filter for visual observing?

    No. Antlia explicitly states this filter is not recommended for night visual observation. It is meant for astrophotography of deep-sky objects that contain SII emission.

    Does the single substrate design of the Antlia 3nm SII Pro help with halos?

    The single, non-glued optical substrate eliminates internal reflections, and the steep spectral profile minimizes halos around bright stars.

    What does the Lambda/4 transmitted wavefront of the Antlia 3nm SII Pro mean for my images?

    A transmitted wavefront of Lambda/4 or better means the filter adds no more than a quarter of a wavelength of wavefront error. Together with parallelism under 30 arcseconds, it is a measure of the filter's optical quality.

  • Filter Type SII Narrowband (3nm Pro series)
    Center Wavelength (CWL) 672.4nm
    Bandpass (FWHM) 3nm
    Peak Transmission >88%
    Transmission Guarantee T>88% within 1nm of center bandwidth
    Out-of-Band Blocking >OD5 (0.001%) @ 300-1000nm
    Recommended F-Ratio Usable down to f/3
    Transmitted Wavefront Lambda/4 or better
    Parallelism < 30 arcseconds
    Surface Quality 60/40 (Scratch/Dig) per MIL-O-13830
    Filter Substrate Single, non-glued optical substrate
    Filter Thickness 2mm ±0.05mm (1.25", 31mm, 36mm, 2"); 3mm ±0.05mm (50mm)
    Edges (Unmounted) Blackened to prevent internal reflections
    Filter Cell (Mounted) Ultra-thin, black anodized, laser engraved
    Mounting Threads 1.25" (M28.5x0.6), 2" (M48x0.75)
    Available Sizes 1.25" Mounted, 31mm Unmounted, 36mm Unmounted, 2" Mounted, 50mm Unmounted
    Not Recommended For Solar imaging, night visual observation

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  • Antlia 3-year warranty against delamination.