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Antlia 2.5nm H-a, SII and OIII Ultra 2'' Narrowband Filters
Antlia 2.5nm H-a, SII and OIII Ultra 2'' Narrowband Filters

Antlia 2.5nm H-a, SII and OIII Ultra 2" Narrowband Filters

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Antlia H-a, SII and OIII 2.5nm Ultra Filter - Extra Narrowband filters   2" mounted

The Antlia SHO 2.5nm Ultra series filters are made with quartz glass and undergo precisely controlled coating processes to ensure optimal performance. The 2.5nm Ultra series is designed with a FWHM (full width half maximum) of 2.5nm +0.3/-0.1nm and a transmission efficiency >93-95% at the Central Wavelength.

The quartz glass possesses an ultra-low thermal expansion coefficient with outstanding thermal and mechanical properties. When combined with advanced coating processes, these filters exhibit remarkable durability for imaging and research in the most challenging environmental conditions.

Compared to the 3nm Pro series, the 2.5nm Ultra series coated on quartz glass exhibits higher transmittance with Ha/SII≥95% and OIII≥93%. These filters are estimated to improve signal by 20-30% in your images. Additionally, the Ultra series boasts a narrower FWHM of 2.5nm+0.3/-0.1nm, resulting in an exceptionally high Signal to Noise Ratio for deep sky photography.

The main features and application:

  • High transmittance (Ha/SII≥95%, OIII≥93%) and the narrow FWHM 2.5nm +0.3/-0.1nm to maximize contrast;
  • Flat-top spectrum minimizes the loss in transmission due to the Centre Wavelength (CWL)-shift;
  • Out of band blocking specification is designed to OD5 (0.001%) to block interference from other wavelengths and minimize halos around bright stars;
  • Made of quartz glass, excellent durability and thermal stability, better fracture resistance and scratch resistance, improved coating resilience to cleaning;
  • Filters are resistant to scratches;
  • Identical filter thickness to existing standards and double-sided fine polishing , with utmost care for parfocality;
  • The SHO 2.5nm Ultra filters are recommended for use in optics with a Focus Ratio of ≥ f/3.5 for best optical performance;
  • 100% of production are scanned individually, all transmission and blocking (OD) data in the box are actual, measured spectra and transmission;
  • All Antlia filters are coated to the edge of the substrate and unmounted narrowband filters are edge blackened to eliminate internal reflections from stray light;
  • Warranty: 3-years against delamination.

Filter Ring:

  • Antlia standard ring:1.25’’ (M28.5*0.6),2’’(M48*0.75)
  • Ultra-thin filter cell to minimize vignetting by maximize possible clear aperture
  • Black Anodized Finish
  • Laser Engraving No Fading

Not Recommended:

  • Solar imaging
  • Night visual observation

Not Permitted:

  • Serious eye damage will result if you fail to observe the warning.

Antlia 2.5nm H-a, SII and OIII Ultra 2" Narrowband Filters H-alpha

Antlia 2.5nm H-a, SII and OIII Ultra 2" Narrowband Filters OIII

Antlia 2.5nm H-a, SII and OIII Ultra 2" Narrowband Filters SII


Specifications: Antlia 2.5nm H-a, SII and OIII Ultra 2" Narrowband Filters




Oxygen III


2.5nm +0.3/-0.1nm

2.5nm +0.3/-0.1nm

2.5nm +0.3/-0.1nm

CWL (Central Wavelength)




Peak Transmission






Filter Thickness



What's in the Box

What's in the Box: Antlia 2.5nm H-a, SII and OIII Ultra 2" Narrowband Filters

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