Everything you need to know about Antlia PRIME 7nm H-Alpha filters
The Antlia 7 mm H-alpha (Ha) filter is suitable for imaging diffuse nebulae, planetary nebulae and Ha-rich supernova afterglow. The 7 nm bandwidth (centered on the H-alpha line at 656.3 nm) gives PRIME filters a wider bandwidth than the EDGE range. Therefore, PRIME filters let a little more signal through... but a little more light pollution. The narrow bandwidth allows deep sky imaging even under very difficult light pollution conditions, and greatly increases the contrast of objects under very dark skies. A large proportion of light pollution lines, particularly from mercury vapor and sodium lamps, are eliminated.
The EDGE range (4.5 nm) and the 3 nm range block ionized nitrogen (NII) lines, unlike the PRIME range, which lets these 2 lines through at 645.8 nm and 658.3 nm.
Antlia PRIME narrowband filters are designed to bring out the faintest details of nebulae by suppressing unwanted wavelengths in the background sky. The narrower the bandwidth, the more effective the filter. The transmission of the filter reaches 95% at 656.3 nm. The optical density outside the transmission area is OD4 (0.01%), which provides an excellent signal-to-noise ratio and a clear cut-off of the other lines. The clear cut-off of the signal outside the transmission zone is an important parameter because it determines the quality of the filtration. The steeper the cutoff slope, the greater the contrast between the H-alpha signal and the perfectly black background sky. In addition, a sharp cut-off minimizes halos around bright stars.
Antlia conducts extremely strict quality control during the manufacturing process. Each filter is tested and measured to ensure that it meets the high performance requirements of the specifications. Tight tolerances require perfectly homogeneous substrates and uniform thicknesses; deviations from specifications should not exceed 0.05 mm.
Applications and performance
- Narrow bandwidth of 7 nm, designed for astronomical imaging of diffuse nebulae, planetary nebulae and supernova afterglow, whatever the sky quality
- Can be combined with Antlia 7nm SII and OIII filters for SHO imaging in the Hubble palette
- Sharp cut-off of unwanted lines around H-alpha. Transmission is 97% at 656.3 nm, which increases the contrast of H-alpha objects.
- Antlia EDGE narrowband filters are compatible with instruments at F/d >2 with slight signal loss.
- All Antlia filters have blackened edges to suppress stray reflections.
- This filter is not suitable for imaging objects that do not emit H-alpha signal, such as galaxies. However, the addition of an H-alpha layer to an LRVB image of a galaxy will bring out the nebulae it contains.
Technical specifications:
- Glass type: Schott optical glass
- Surface quality: 60/40 (according to MIL-O-13830)
- Mounting diameter: 36mm circular without mount
- Substrate thickness: 2 mm
- Transmission: 95% transmission on 656.3nm H-Alpha line
- Treatments: 2-sided polished filter with λ/4 accuracy
- Coating: Multilayer and anti-reflective on 2 faces
