Antlia ALP-T Dualband 5nm Ha/OIII Filter

Dual-Band 5nm Capture for One-Shot Color Cameras

This filter is engineered to capture both the red Hydrogen-alpha line and the blue-green Oxygen III line in a single exposure. For an imager using a DSLR, CMOS, or CCD color camera, this means you can record the two main emission nebula bands at the same time. The narrow 5nm Full-Width at Half-Maximum (FWHM) for both lines provides high-contrast views by isolating the nebula's signal from background light pollution, moonlight, and natural airglow.

By capturing cleaner data in a single session, the filter reduces the post-processing effort required to separate faint details from a washed-out skyglow. Independent sample images with this filter, of the Horsehead and Flame, the Rosette Nebula (NGC 2244) and the Western Veil, were taken under Bortle 5 skies with a 130mm f/5 reflector.

92% Ha / 88% OIII Transmission with OD4.5 Blocking

The ALP-T filter delivers high transmission rates where it counts, with 92% peak transmission for the 656.3nm H-alpha line and 88% for the 500.7nm OIII line. Outside of these narrow 5nm passbands, the filter provides deep blocking with an optical density of OD4.5 or greater. This level of attenuation blocks over 99.99% of unwanted light across a wide spectrum from 300nm in the ultraviolet to 1100nm in the near-infrared.

• Light Pollution Rejection: The filter is designed to suppress artificial lighting effectively in environments from Bortle 8 city skies to Bortle 1 dark sites.
• Deep NIR Blocking: Near-infrared is blocked up to 1100nm.
• High Signal-to-Noise: By combining high transmission of the desired signal with deep blocking of background noise, the filter produces images with a superior signal-to-noise ratio and enhanced contrast.

Ion Gun Deposition on a 2mm Polished Substrate

An Ion Gun Assisted Deposition coating process on a double-sided polished substrate gives consistent, accurate light pollution suppression. The filter has an ideal flat-top, moderate bandpass that reduces spectrum down shifts, and extremely steep bandpass edges that minimize internal reflections.

The filter is 2mm thick (+/- 0.05mm). The filter is housed in an ultra-thin, black-anodized cell with M48x0.75 threads, designed to maximize the clear aperture and minimize vignetting in 2" focusers and filter wheels.

Imaging Workflow: Use with OSC vs. Monochrome Cameras

While engineered specifically for one-shot color cameras, the Antlia ALP-T Ha/OIII filter is also a useful tool for monochrome imagers. Using it with a mono camera allows you to capture both Ha and OIII signal in a single grayscale image, effectively saving imaging time.

For its primary intended use with color cameras, the filter simplifies the imaging process significantly. Instead of requiring a filter wheel and multiple sets of exposures for each narrowband channel, you can gather all the data needed for a full-color Ha/OIII image in a single, continuous session.

4-Band Imaging with the Antlia ALP-T SII/Hb Filter

For imagers wanting to capture a complete four-channel narrowband dataset with a color camera, pair this Ha/OIII filter with the Antlia ALP-T Dual Band 5nm SII&Hb Filter. This two-filter combination allows you to collect data from all four major emission nebula lines: Hydrogen-alpha, Oxygen III, Sulphur II, and Hydrogen-beta.

The workflow involves capturing one set of exposures with the Ha/OIII filter, then swapping it for the SII/Hb filter to capture a second set. In post-processing, the color channels from both datasets can be separated to isolate the individual narrowband signals. This opens up advanced processing possibilities, including creating SHO "Hubble Palette" images or custom color combinations, all without needing a monochrome camera and filter wheel.