Antlia 3nm Narrowband OIII Pro Filter

3nm Bandpass at 500.7nm

The core of this filter's design is its 3nm Full Width at Half Maximum (FWHM) bandpass, centered precisely on the 500.7nm line of doubly ionized oxygen. Targets include OIII emission nebulae, planetary nebulae, Wolf-Rayet nebulae and supernova remnants, and the filter is only effective on deep-sky objects that contain OIII emission. It can be used in light-polluted areas and at dark sites and extends imaging time when the moon is up.

>88% Transmission Guaranteed for Systems Down to f/3

Peak transmission is above 88%, with T>88% guaranteed within 1nm of the center bandwidth. On fast optical systems the steep light cone shifts a filter's central wavelength toward shorter wavelengths (blue shift); conventional broader narrowband filters lose a lot of transmission from this shift, and blue-shift data shows the 3nm Pro can be used with nearly all systems as fast as f/3 with minimal loss in emission signal.

OD5 Blocking from 300-1000nm

To ensure the OIII signal is not contaminated by other light sources, the filter provides out-of-band blocking rated at >OD5. This means the filter transmits less than 0.001% of light outside its narrow passband across a vast range from 300nm to 1000nm. This delivers an excellent signal-to-noise ratio (SNR) and an effective cut-off that minimizes interference from other wavelengths, and its optical reliability reduces post-processing.

Lambda/4 Single-Substrate Optics: Halos and Reflections Minimized

Each filter is built on a single, non-glued optical substrate with a transmitted wavefront of Lambda/4 or better, parallelism of less than 30 arcseconds and 60/40 scratch/dig surface quality per MIL-O-13830.

• Single Substrate: A single substrate eliminates internal reflections.
• Steep Spectral Profile: The steep spectral profile minimizes halos around bright stars.
• Edge Blackening: All unmounted Antlia narrowband filters have their edges blackened to prevent internal reflections from stray light entering the side of the filter.

Mounted and Unmounted Sizes for Any Imaging Train

We offer the Antlia 3nm OIII Pro in five sizes. Mounted versions have an ultra-thin, black-anodized, laser-engraved cell that minimizes vignetting, and screw in by a male thread.

• Mounted Formats: 1.25" (M28.5x0.6) and 2" (M48x0.75).
• Unmounted Formats: 31mm, 36mm and 50mm, with blackened edges.
• Thickness: 2mm (+/- 0.05mm) for 1.25", 2", 31mm and 36mm; 3mm (+/- 0.05mm) for 50mm.

3nm Pro vs. Wider Filters: The Contrast and Exposure Trade-Off

As the bandwidth becomes narrower, contrast on emission targets improves because less background signal gets through. A 3nm band passes less skyglow and moonlight around the OIII line than a 5nm or 7nm band.

The emission line itself is far narrower than 3nm, so it passes either way; what changes is how much background comes with it. Broader filters also lose more transmission from the CWL shift on fast optics.