Filter Quad Band - Antlia

The Antlia "4-band" filter is designed to suppress a significant portion of light pollution for one-shot color cameras (OSCs), such as color astrophotography cameras, digital cameras, and monochrome cameras. Antlia proposes preserving four major emission lines: H-Beta (486.1 nm), OIII (495/500 nm), H-Alpha (656.3 nm), and S-II (672 nm), with narrowed bandwidths. Additionally, a 400 nm (blue) region helps maintain good color balance. A wide area in the near-infrared (NIR) from 760 to 920 nm is included due to the high sensitivity of current cameras in this spectral region.

The Antlia "Quad-Band" filter is therefore more selective than conventional RGB filters, which do not block light pollution, while also being brighter than interference filters such as H-Alpha, SII, and OIII. It is thus compatible with imaging galaxies and clusters (which radiate across the entire visible spectrum). Antlia estimates that 95% of objects are photographable in skies with a Bortle scale value between 1 and 8. Another important aspect of this particular filter is the clear cutoff of each zone and its compatibility with instruments having an ultra-short focal ratio down to f/2.

The idea is to block as much as possible the emission peaks from mercury (Hg) and sodium (Na) lamps, which heavily pollute our skies.

The radiation from nebulae in Hbeta, OIII, H-Alpha, and SII is transmitted at over 93%, and the cutoff slopes are sharp. Although the colorimetry of galaxies is altered (they radiate across the entire spectrum, unlike nebulae which emit primarily in a specific spectral region), this type of filter is very well suited. The same applies to globular clusters.

Applications and Performance

• Designed specifically for use with color DSLR cameras, CMOS and CCD cameras, and monochrome sensors. Optical density (OD) suppression at unwanted visual wavelengths increases the signal-to-noise ratio.
• For imaging nebulae, galaxies, and star clusters.
• Extremely steep line cutoffs minimize internal reflections.
• Ion gun-assisted deposition coating technology on the double-sided polished substrate makes this the most consistent and accurate light pollution suppression filter.
• Good performance at focal ratios greater than f/2, with contrast increasing with the focal ratio.
• Designed to suppress a significant portion of artificial illumination on the Bortle scale 1 to 8. Near-infrared (NIR) is blocked up to 1100 nm.
• Transmission rate greater than 93% for H-alpha, SII, NII, and OIII lines.
• 2" (50.8 mm) barrel with M48 thread.