Antlia’s Oiii 2.5nm Ultra Series filter is built with high-quality quartz glass and manufactured using tightly controlled coating processes to deliver top-tier performance. The Ultra Series features a full width at half maximum (FWHM) of 2.5nm (+0.3/-0.1nm) and achieves a transmission efficiency greater than 92–95% at the central wavelength.

The quartz glass used in these filters offers an ultra-low thermal expansion coefficient, along with excellent thermal and mechanical stability. This, combined with advanced coating technology, gives the filters outstanding durability—making them ideal for demanding imaging and research conditions.

Compared to the 3nm Pro Series, the 2.5nm Ultra Series filters offer higher transmittance across key emission lines. They reach ≥95% transmission at the Oxygen line 500.7nm. This increase in efficiency can boost signal strength by an estimated 20–30% in your images.

With its narrower 2.5nm bandwidth, the Ultra Series filters also deliver an exceptionally high signal-to-noise ratio—perfect for capturing fine detail in deep-sky astrophotography.

Application and Performance:

• Achieves high transmittance rates — Oxygen(Oiii) ≥92% — with a narrow 2.5nm FWHM (+0.3/-0.1nm) to maximise contrast

• Utilises a flat-top spectral profile to reduce transmission loss caused by centre wavelength (CWL) shift

• Provides out-of-band blocking at OD5 (0.001%) to minimise interference from adjacent wavelengths and suppress halos around bright stars

• Constructed from premium quartz glass for outstanding durability, thermal stability, and superior resistance to scratches and fractures

• Offers enhanced coating resilience for easier and safer cleaning

• Maintains standard filter thickness with double-sided fine polishing to ensure parfocal compatibility across filter sets

• Designed for best performance in optical systems with a focal ratio of f/3.5 or slower

• Every filter undergoes 100% individual spectral testing, with measured transmission and OD data included in the box

• All Antlia filters are edge-coated, and unmounted filters are edge-blackened to eliminate internal reflections from stray light

• Backed by a 3-year warranty against delamination

The filter ring features a 2″ (M48×0.75) thread. Its ultra-thin filter cell maximises the clear aperture and helps minimise vignetting in fast optical systems. A durable black anodised finish protects the housing, while laser-engraved markings ensure long-term visibility without fading.

Important: This filter isn’t suitable for solar imaging or night-time visual observation.

Warning: Never look directly at the Sun using this filter. Ignoring this safety warning can result in serious and permanent eye damage.

Antlia also offers dual narrowband filters designed specifically for one-shot colour (OSC) cameras. These include the ALP-T Dualband Ha&OIII 3nm and the SII&Hb 3.5nm filters. When used together, they enable the capture of narrow-band spectral data across four channels—H-alpha, OIII, SII, and H-beta. You can separate and recombine these channels during post-processing to create a wide range of colour palettes. This flexibility allows you to boost luminance contrast in RGB-balanced images or produce false-colour combinations such as H-O-Hb, S-H-O, H-S-OHb, and H-O-O to suit your creative and scientific goals.