Filter ANTLIA H-ALPHA 3nm Pro Series - 50mm circular unmounted model

The Antlia 3nm H-alpha (Ha) filter is suitable for imaging diffuse nebulae, planetary nebulae and Ha-rich supernova afterglow. The 3 nm bandwidth is centered on the H-alpha line at 656.3 nm. The thinness of the bandwidth allows deep sky imaging even in very difficult light contamination conditions, and greatly increases the contrast of objects in very dark skies. All stray lines of light pollution, including those from mercury vapor and sodium lamps, are eliminated.

Narrow-band Antlia filters are designed to bring out the faintest details of nebulae by removing unwanted wavelengths from the sky background. The narrower the bandwidth, the more effective the filter. Filter transmission reaches 90% at 656.3 nm. The optical density outside the transmission zone is OD3 (0.1%), 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 higher the cut-off slope, the higher the contrast between the H-alpha signal and the sky background, which has become perfectly black. In the case of the H-alpha filter, this means that the signal of the NII line (658.4 nm), which is very close to H-alpha, is strongly excluded. In addition, a sharp cutoff minimizes halos around bright stars.

Antlia performs 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

• Very narrow bandwidth of 3nm, designed for astronomical imaging of diffuse nebulae, planetary nebulae and supernova afterglow, whatever the sky quality.
• Can be combined with Antlia 3nm SII and OIII filters for SHO imaging in the Hubble palette.
• Sharp cut-off of unwanted lines around H-alpha. The transmission of the NII line at 658.4 nm is greatly reduced (only 50% transmission), while it is fully included with other less selective filters. Transmission is 90% at 656.3 nm, which increases the contrast of H-alpha emitting objects.
• All Antlia filters have blackened edges to suppress parasitic reflections.
• This filter is not suitable for imaging objects that do not emit H-alpha signal, such as galaxies. However, adding an H-alpha layer to an LRVB image of a galaxy will highlight the nebulae it contains.

Technical specifications

• Lens type: Schott optical glass
• Surface Quality: 60/40 (according to MIL-O-13830)
• Mounting diameter 50mm circular without mount
• Substrate thickness 3mm
• Transmission 90% transmission in the H-Alpha line of 656.3nm
• Treatments Filter polished on 2 sides with λ/4" accuracy
• Multilayer anti-reflective coating on 2 sides