Antlia ALP-T Dualband 5nm Ha/OIII Highspeed Filter

Dual 5nm Bandpasses with 88% and 82% Transmission

This filter captures the two most important emission nebula bands simultaneously: Hydrogen-alpha at a central wavelength (CWL) of 657.8nm and Oxygen-III at 502.2nm. By using narrow 5nm full-width half-maximum (FWHM) windows for both, it isolates the specific light from nebulae while rejecting unwanted background signal from moonlight, airglow, and artificial lighting.

The design achieves a peak transmission of 88% for the red H-alpha line and 82% for the blue-green OIII line.

Engineered for Fast Optics: f/2.2 to f/3.6

The "Highspeed" designation indicates that this filter is specifically designed to counteract the blue-shifting effect inherent in fast optical systems. Antlia has shifted the central wavelengths of the passbands to compensate, ensuring peak performance for telescopes with focal ratios between f/2.2 and f/3.6. Within this range, the filter delivers stronger and more contrasted nebula images compared to a standard dual-band filter.

With optics faster than f/2.2 a narrowband filter's band shifts to shorter wavelengths and transmission at the emission line may drop by perhaps 15-20%, and the Highspeed filter is affected similarly. User data shows the filter still increases emission nebula contrast and minimizes halos on such optics, and the Highspeed version is still preferred over the standard version on optics faster than f/2.2.

OD4.5 Blocking for Bortle 1-8 Skies

The core of the ALP-T's performance is its aggressive suppression of unwanted light. With a blocking depth of Optical Density 4.5 (OD4.5) or greater, it passes about 0.003% of unwanted wavelengths from 300nm to 1050nm, suppressing light pollution, moonlight and airglow.

• Broad Spectrum Rejection: Blocking is rated from 300nm and near-infrared is blocked up to 1050nm.
• Bortle Scale Efficacy: The filter is designed to be effective in environments from Bortle 1 to Bortle 8.

2mm Substrate with Ion-Assisted Coatings

Each filter is built on a double-sided polished substrate with a thickness of 2mm (±0.05mm). The advanced multi-layer coatings are applied using Ion Gun Assisted Deposition technology. Antlia uses the process for consistent, accurate light pollution suppression.

The flat-top, moderate bandpass reduces spectrum down shifts. Each filter is inspected and measured with a professional spectrophotometer at a resolution of up to 0.2nm.

OSC and Monochrome Camera Integration

While designed primarily for one-shot color (OSC) cameras like DSLRs and dedicated astronomy cameras, the ALP-T Highspeed filter is also a useful tool for monochrome imagers. It can be used as a narrowband filter for monochrome cameras to save imaging time.

• For OSC Cameras: The filter passes red H-alpha light to your camera's red pixels and blue-green OIII light to the green and blue pixels. This allows you to create a detailed, high-contrast color image of emission nebulae from a single imaging session.
• For Monochrome Cameras: When used with a mono camera, both emission lines are recorded together as a single luminance channel. Note that the Ha and OIII signals cannot be separated in post-processing when captured this way.

ALP-T Highspeed vs. Standard: Choosing for Your f-Ratio

The choice between Antlia's Highspeed and standard ALP-T filters is determined entirely by the focal ratio of your imaging system. Using the correct filter for your telescope's f-ratio is critical for achieving maximum signal.

• Choose this Highspeed Version if: Your optical system has a focal ratio between f/2.2 and f/3.6. The Highspeed version produces much stronger and more contrasted nebula images than the standard version in this range.
• Choose the Standard ALP-T Version if: Your optical system is slower than f/3.6. For telescopes like f/5 Newtonians, f/7 refractors, or f/10 SCTs, Antlia highly recommends the standard ALP-T 5nm filter to ensure the passbands are correctly aligned with the emission lines.