Antlia 2.5nm OIII Ultra Series Filter - 2" - OIII-ULTRA-2.5NM-2

This very narrowband 2.5 nm OIII filter from Antlia is part of their Ultra series and comes in a 2" threaded filter cell that is designed to be screwed on to the 2" receptacle of your astrophotography accessory, including a 2" filter wheel or filter drawer.  

Antlia 2.5nm Ultra Series OIII Filter - 2" Mounted

All Antlia 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 >92-95% 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≥92%. 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.

Important:  Do not use when viewing or imaging the Sun!

Highlights & Application 

- High transmittance （Ha/SII≥95%，OIII≥92%）and the narrow FWHM 2.5nm +0.3/-0.1nm to maximize contrast;

- Flat-top spectrum minimizes the loss in transmission due to the Center 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 de-lamination.

Oxygen III Filter Tech Specs:

FWHM:  2.5nm +0.3/-0.2nm

CWL (Central Wavelength): 500.7nm

Peak Transmission:  92%

Blocking:  +/-OD5

Filter Thickness:  2 mm +/- 0.05mm

Filter Ring:

Antlia standard ring: 2’’(M48*0.75)

Ultra-thin filter cell to minimize vignetting while maximizing clear aperture 

Black Anodized Finish

Laser Engraving No Fading