The Antlia H-alpha Pro Highspeed 3 nm filter is designed for astrophotography with fast instruments that have a focal ratio between f/2.6 and f/3.6. It features a 3 nm bandwidth, with a shifted central wavelength to compensate for the behavior of interference filters in a highly convergent beam.
Price range: CHF 278.85 through CHF 360.36
The Antlia H-alpha Pro Highspeed 3 nm filter is designed for astrophotography with fast instruments that have a focal ratio between f/2.6 and f/3.6. It features a 3 nm bandwidth, with a shifted central wavelength to compensate for the behavior of interference filters in a highly convergent beam.
As the angle of incidence of light increases, the transmission band of an interferential filter shifts toward shorter wavelengths. Antlia pre-shifts this band by 1.2 nm toward the red to compensate for this phenomenon. For the H-alpha model, the specified central wavelength is 657.5 nm. This value applies to the Highspeed version and should not be confused with that of the standard Pro filter. The peak transmission listed in the manufacturer’s table is 90 %.
Antlia recommends this series for apertures between f/2.6 and f/3.6 to improve signal collection from nebulae compared to the standard version under these conditions. For focal ratios higher than f/3.6, the manufacturer recommends the standard Pro 3 nm filters. For instruments faster than f/2.6, Antlia recommends the EDGE 4.5 nm series. The Highspeed version is therefore not presented as the default choice for all telescopes: the focal ratio is a determining factor.
The options listed on this product page are the mounted 2″ filter and the unmounted 36 mm disc. The 2″ version features an M48 × 0.75 thread and a black anodized thin mount. The 36 mm disc is designed for use with a mount compatible with unmounted filters; its edges are blackened to minimize stray reflections. Both sizes use 2 mm ± 0.05 mm glass. Each option corresponds to the filter for the line indicated in the title, not the complete set of H-alpha, OIII, and SII filters.
Out-of-band blocking is specified to be at least OD5 between 300 and 1000 nm. The unique, unglued optical substrate and sharp cutoff profile are designed to reduce internal reflections and halos around bright stars. Documented applications include emission nebulae, planetary nebulae, and Wolf-Rayet nebulae, as well as supernova remnants. Antlia does not recommend nighttime visual observation or solar imaging with this filter. Never use it to view the Sun.
| Stingray | H-alpha |
|---|---|
| Center wavelength | 657.5 nm |
| Bandwidth FWHM | 3 nm |
| Peak Transmission | 90 % |
| Blocking | ≥ OD5, 300 to 1,000 nm |
| Recommended Focus Report | f/2.6 to f/3.6 |
| Thickness | 2 mm ± 0.05 mm |
| Formats | 2″ mounted; 36 mm unmounted |
