Antlia, a prominent manufacturer of astronomical imaging filters, has announced the release of a new ultra-narrowband filter designed for One-Shot Color (OSC) cameras. The ALP-T 3nm SII & OIII filter is the latest addition to the company’s growing ALP-T dual-band series, offering astrophotographers enhanced capabilities for capturing detailed images of emission nebulae.
The new filter isolates two key emission lines—Sulfur-II (672.4nm) and Oxygen-III (500.7nm)—with a narrow 3nm bandwidth, enabling OSC users to achieve high-contrast, narrowband images typically associated with monochrome camera systems. This development marks a significant step in making advanced imaging techniques more accessible to a broader range of astrophotographers.
Narrowband Imaging for Color Cameras
Narrowband filters are essential tools for imaging faint deep-sky objects, particularly in light-polluted environments. Unlike broadband filters, which capture a wide range of wavelengths, narrowband filters isolate specific emissions from ionized gases. This allows for greater contrast and detail, especially in nebulae.
The ALP-T 3nm SII & OIII filter enables simultaneous capture of both emission lines using a single OSC sensor. Sulfur-II emissions often reveal structural features not visible in other bands, while Oxygen-III highlights delicate, oxygen-rich regions. The dual-band design simplifies the imaging process for OSC users, reducing the need for complex channel extraction.
Technical Specifications
The filter is engineered with several advanced features, including:
- 3nm Full Width at Half Maximum (FWHM) for both SII and OIII
- High optical density (≥OD4.5) for effective light pollution suppression
- Multi-layer coatings with halo suppression and anti-reflective properties
- Ion Gun Assisted Deposition (IAD) for durability and coating consistency
- Standard 2″ mounted format with M48x0.75 thread and ultra-thin cell to minimize vignetting
Estimated peak transmission rates are approximately 90% for SII and 82% for OIII, based on similar filters in the ALP-T series.
Considerations for Users
While the filter offers significant advantages, users should be aware of a few considerations. The narrow 3nm bandwidth may require longer exposure times, especially for the fainter SII signal. Additionally, halos around bright stars—a common challenge in narrowband imaging—may still occur, though Antlia’s coatings aim to minimize this effect.
The filter is optimized for telescopes with focal ratios slower than f/4. Users with faster optics are advised to check for potential bandpass shifts or consider high-speed variants.
A Broader Commitment to OSC Imaging
With the release of the ALP-T 3nm SII & OIII filter, Antlia continues to expand its ecosystem of narrowband solutions for OSC users. The company’s growing lineup now includes filters for Ha, OIII, SII, and Hb, offering a comprehensive toolkit for capturing the full spectrum of nebular emissions.