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Antlia SII 2.5nm Ultra Narrowband Filter
Antlia SII 2.5nm Ultra Narrowband Filter
Antlia SII 2.5nm Ultra Narrowband Filter
Antlia SII 2.5nm Ultra Narrowband Filter
Antlia SII 2.5nm Ultra Narrowband Filter
Antlia SII 2.5nm Ultra Narrowband Filter

Antlia SII 2.5nm Ultra Narrowband Filter

by Antlia
SKU ANT-SII-2.5NM-RD36
CA$651.00 - CA$826.00
CA$651.00
CA$651.00 - CA$826.00
CA$651.00
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  • Isolates Sulfur-II emission at 671.6nm and 673.1nm
  • Ultra-narrow 2.5nm FWHM bandpass
  • Peak transmission of >=95%
  • Out-of-band blocking at >=OD5 (0.001%)
  • 2mm quartz glass substrate
  • Recommended for optical systems f/3.5 or slower
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  • Description
  • FAQ
  • Specifications
  • In the Box
  • Warranty

  • Antlia SII 2.5nm Ultra Narrowband Filter

    The Antlia SII 2.5nm Ultra Narrowband Filter passes the 671.6nm and 673.1nm sulfur-II lines through a 2.5nm (+0.3/-0.1nm) full width at half maximum (FWHM), with peak transmission of 95% or more and OD5 (0.001%) out-of-band blocking. It is coated on 2mm quartz glass. Use it with optics of f/3.5 or slower; the narrow FWHM gives an exceptionally high signal-to-noise ratio for deep-sky photography.

    Core Optics: 2.5nm Bandpass and >=95% Peak Transmission

    At 2.5nm, the band passes the SII lines with less moonlight and artificial light around them than a wider band. The high transmittance and narrow FWHM maximize contrast.

    This narrow bandpass is paired with a high peak transmission of >=95% at the 671.6nm and 673.1nm lines. Compared with the 3nm Pro series, the Ultra filters have higher transmittance for the emission lines and are estimated to improve signal by 20-30% in your images.

    Signal Integrity: >=OD5 Blocking and Flat-Top Spectrum Profile

    Blocking is optical density 5 (OD5) or better, designed to block interference from other wavelengths and minimize halos around bright stars.

    The flat-top spectrum minimizes the loss in transmission due to the CWL shift that converging light causes.

    2mm Quartz Glass Substrate

    Antlia coats the 2.5nm Ultra series on quartz glass, which it says has an ultralow thermal expansion coefficient, outstanding thermal and mechanical properties and better fracture and scratch resistance, with coatings more resilient to cleaning.

    • Thickness: 2mm (+/-0.05mm on the 2" mounted, +/-0.1mm on the 36mm). The thickness is identical to existing standards, with double-sided fine polishing and utmost care for parfocality.
    • Edge Blackening: All filters are coated to the edge of the substrate, and unmounted versions are edge-blackened to eliminate internal reflections from stray light.
    • Quality Control: 100% of production is scanned individually, and the transmission and blocking data are actual, measured spectra.

    2.5nm Ultra Compared with the 3nm Pro

    The Ultra has a narrower 2.5nm band, is coated on quartz glass and transmits 95% or more at the SII lines, against 3nm and 88% for the 3nm Pro. Antlia estimates a 20-30% signal improvement. The 3nm Pro is rated down to f/3, the Ultra for f/3.5 or slower.

    A narrower band passes less of the continuous skyglow around the lines, so the background is darker on emission nebulae such as the Soul (IC 1848) or the Rosette (NGC 2237).

  • What is the main advantage of the Antlia SII 2.5nm Ultra filter over a 3nm filter?

    Compared with Antlia's 3nm Pro series, the 2.5nm Ultra has a narrower band and higher transmittance (95% or more against 88%) on quartz glass, and Antlia estimates a 20-30% signal improvement. The narrower band also passes less background light.

    Will the Antlia SII 2.5nm filter work with my fast f/4 telescope?

    Yes. The 2.5nm Ultra is recommended for f/3.5 or slower, and f/4 is slower than that. Its flat-top spectrum minimizes the transmission loss from the blue shift of converging light.

    Why does the Antlia SII 2.5nm Ultra use a quartz glass substrate?

    Quartz glass has an ultralow thermal expansion coefficient and outstanding thermal stability, and gives excellent durability, better fracture and scratch resistance and coatings more resilient to cleaning.

    How does the Antlia SII 2.5nm filter perform on the Wizard Nebula (NGC 7380) from the suburbs?

    The Wizard Nebula is an emission nebula with sulfur-II emission. The 2.5nm band passes the 671.6nm and 673.1nm lines with little of the surrounding broadband light pollution, so the background is darker.

    What does >=OD5 blocking mean for my images with the Antlia SII 2.5nm filter?

    OD5 blocking means the filter reduces out-of-band light to just 0.001% of its original intensity (a factor of 100,000). This blocks interference from other wavelengths and minimizes halos around bright stars.

    Is the Antlia SII 2.5nm Ultra filter parfocal with other Antlia filters?

    Antlia manufactures the SII 2.5nm Ultra filter to a thickness of 2mm, which is consistent across the H-alpha and OIII filters in the 2.5nm Ultra series, and they are made with care for parfocality. Check focus when mixing filters from different series.

    Can I use the Antlia SII 2.5nm filter for visual observing?

    No. Night visual observation and solar imaging are not recommended. Do not look at the Sun with this filter.

  • Filter Type SII Ultra Narrowband (SHO 2.5nm Ultra Series)
    Central Wavelength (CWL) 671.6nm / 673.1nm
    Peak Transmission >=95% at 671.6nm / 673.1nm
    FWHM (Bandwidth) 2.5nm (+0.3/-0.1nm)
    Blocking >=OD5 (0.001%) out-of-band
    Spectrum Profile Flat-Top
    Recommended F-Ratio f/3.5 or slower
    Substrate Quartz Glass
    Filter Thickness 2mm (+/-0.05mm on 2" mounted, +/-0.1mm on 36mm unmounted)
    Surface Quality Double-sided fine polishing
    Edge Treatment Coated to the edge; unmounted filters are edge blackened
    Mounting (2" Version) M48x0.75 threads, ultra-thin black anodized cell, laser engraved
    Available Sizes 36mm Round Unmounted, 2" Mounted
    Quality Control 100% of production scanned individually
    Not Recommended For Solar imaging, night visual observation

    • Antlia SII 2.5nm Ultra filter (selected size)

      × 1

    • Protective case

      × 1

  • Antlia 3-year warranty against delamination.