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Antlia ALP-T Dual Band SII&Hβ 3.5nm

Antlia ALP-T Dual Band SII&Hβ 3.5nm

by Antlia
SKU ANT-ALP-T-3NM-SIIHB
$360.00 - $360.00
$360.00
$360.00 - $360.00
$360.00
Price Match Policy!
  • Dual-band filter passing Sulfur-II (672.4nm) and Hydrogen-beta (486.1nm)
  • 3.5nm (+/-0.5nm) FWHM on both lines
  • Peak transmission of 90% (SII) and 85% (H-beta)
  • ≥OD4.5 blocking from 300-1100nm; designed for Bortle 1 to 8 skies
  • Best performance with optics slower than f/4
  • 2mm single, non-glued Lambda/4 substrate; 2" mounted, male M48x0.75 thread
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  • Description
  • FAQ
  • Specifications
  • In the Box
  • Warranty

  • Antlia ALP-T Dual Band SII&Hβ 3.5nm Filter - 2" Mounted

    The Antlia ALP-T Dual Band SII&Hβ 3.5nm filter isolates two key emission lines on a single 2mm substrate, passing the deep-red Sulfur-II line at 672.4nm and the blue Hydrogen-beta line at 486.1nm. With a tight 3.5nm full width at half maximum (FWHM), it blocks unwanted light at ≥OD4.5. Peak transmission is 90% for SII and 85% for H-beta. Antlia designed it primarily for color cameras.

    A 3.5nm Dual-Bandpass Filter for SII & H-beta

    This filter is engineered to capture two specific spectral lines simultaneously: the deep-red Sulfur-II line at 672.4nm and the often-overlooked Hydrogen-beta line at 486.1nm. The 3.5nm bandpass passes only the SII and H-beta signal, blocking light pollution, moonlight and airglow and enhancing nebula contrast.

    While H-alpha is the dominant hydrogen emission, H-beta, the second most common hydrogen emission, can reveal structures not seen in OIII. Combined with data from the Ha/OIII filter it completes a four-channel set.

    90% Transmission and OD4.5 Light Pollution Blocking

    Peak transmission is 90% at the SII line and 85% at H-beta. The filter provides suppression of unwanted wavelengths, including artificial lighting and natural airglow, at an optical density of ≥OD4.5 across a wide spectrum from 300nm to 1100nm.

    • Deep Blocking: The ≥OD4.5 rating means at most about 0.003% of unwanted light is passed.
    • Bortle 1-8: Antlia designed it to suppress artificial lighting from Bortle 1 to Bortle 8.
    • Near-IR Suppression: Near-infrared is blocked up to 1100nm.

    Optimizing for Systems Slower than f/4

    The filter is recommended for optics slower than f/4 for best performance. On faster optics the steeper light cone shifts the bandpass to shorter wavelengths, which can reduce transmission at the emission lines.

    For optics faster than f/4, a pre-shifted highspeed version is a better choice.

    Lambda/4 Substrate with Ion-Assisted Coatings

    Antlia builds the ALP-T filter on a single, non-glued optical substrate with a thickness of 2mm. The surface is polished to a transmitted wavefront of Lambda/4 or better and parallelism of less than 30 arcseconds, with surface quality of 60/40 scratch/dig (MIL-O-13830).

    The advanced coatings are applied using an Ion Gun Assisted Deposition process, and the coating technology makes durability very reliable. The filter has an ideal flat-top, moderate bandpass that reduces spectrum downshifts, and a halo suppression anti-reflective coating that minimizes halos and internal reflections.

    The 4-Channel Workflow: Pairing the SII&Hβ with the Ha&OIII Filter

    The Antlia ALP-T SII&Hβ filter is designed as a direct complement to its sibling, the Antlia ALP-T Ha&OIII filter. Using both filters allows astrophotographers with one-shot-color (OSC) cameras to capture spectral data from four channels.

    By capturing data with both filters, you acquire separate signals for H-alpha, Oxygen-III, Sulfur-II, and Hydrogen-beta. This comprehensive dataset can then be separated in post-processing and recombined into a variety of popular false-color palettes, such as SHO (the "Hubble Palette") or H-O-Hb.

  • Why does the Antlia ALP-T filter pair SII with H-beta instead of OIII?

    This design decision allows imagers to capture unique structural details. Capturing more OIII boosts an existing signal but adds no new information, and an RGGB Bayer matrix, with twice as many green pixels, already improves OIII capture with the Ha/OIII filter. H-beta, the second most common hydrogen emission, can reveal structures not seen in OIII in nebulae that contain some blue emission.

    What f-ratio suits the Antlia ALP-T 3.5nm SII&Hβ filter?

    The filter is specified for best performance on optical systems with f-ratios slower than f/4. On faster systems the steeper light cone shifts the bandpass and can reduce signal. For optics faster than f/4, a pre-shifted highspeed version is a better choice.

    How do I use the Antlia ALP-T SII&Hβ filter with my color (OSC) camera?

    Its main use is to capture data that can be combined with data from an Antlia ALP-T Ha&OIII filter. This two-filter approach lets you gather all four major narrowband emission lines (Ha, OIII, SII, Hβ) with your color camera. You can then separate these channels during processing to create detailed false-color images.

    Can I use the Antlia ALP-T 3.5nm filter for visual observation?

    No, this filter is not recommended for visual use. Night visual observation is not recommended; the filter is made for imaging with a camera.

    How does this filter help with imaging from my Bortle 8 backyard?

    Antlia designed it to suppress artificial lighting from Bortle 1 to Bortle 8. With ≥OD4.5 blocking and 3.5nm bands, it passes only light close to 672.4nm and 486.1nm, blocking most light pollution, moonlight and airglow.

    Is the Antlia ALP-T SII&Hβ filter safe for solar imaging?

    Absolutely not. Solar imaging is not recommended. Warning: do not look at the Sun with this filter directly; serious eye damage will result if you fail to observe the warning.

  • Filter Type Dual-band (SII / H-beta)
    Central Wavelength (CWL) 672.4nm (SII) / 486.1nm (H-beta)
    FWHM 3.5nm +0.5/-0.5nm
    Peak Transmission 90% (SII) / 85% (H-beta)
    Blocking ≥OD4.5 @ 300-1100nm
    Filter Thickness 2mm +/-0.05mm
    Substrate Optical, single / non-glued substrate
    Surface Quality (S/D) 60/40 (MIL-O-13830)
    Transmitted Wavefront Lambda/4 or better
    Parallelism less than 30 arcsec
    Recommended F-Ratio Slower than f/4 for best performance
    Filter Ring 2" mounted, M48x0.75 thread
    Not Recommended For Solar imaging, night visual observation

    • Antlia ALP-T Dualband 3.5nm SII&H-beta filter, 2" mounted

      × 1

    • Protective case

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  • Contact us for warranty details.