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Antlia 3nm Narrowband H-alpha Pro Highspeed Filter - f/2.6 to f/3.6
Antlia 3nm Narrowband H-alpha Pro Highspeed Filter - f/2.6 to f/3.6
Antlia 3nm Narrowband H-alpha Pro Highspeed Filter - f/2.6 to f/3.6
Antlia 3nm Narrowband H-alpha Pro Highspeed Filter - f/2.6 to f/3.6
Antlia 3nm Narrowband H-alpha Pro Highspeed Filter - f/2.6 to f/3.6

Antlia 3nm Narrowband H-alpha Pro Highspeed Filter - f/2.6 to f/3.6

by Antlia
SKU ANT-HA-3NM-HS-1.25
CA$375.00 - CA$721.00
CA$375.00
CA$375.00 - CA$721.00
CA$375.00
Price Match Policy!
  • Optimized for fast optical systems from f/2.6 to f/3.6
  • 3nm bandpass (FWHM) around the H-alpha line
  • Center wavelength pre-shifted 1.2nm to the red (657.5nm) to compensate for blue shift
  • Peak transmission 90%
  • OD5 (0.001%) blocking from 300-1000nm suppresses unwanted wavelengths
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Vignetting Calculator

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Check which filter and adapter sizes clear the sensor with the Antlia 3nm Narrowband H-alpha Pro Highspeed Filter - f/2.6 to f/3.6, and how much light the corners lose.

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  • Description
  • FAQ
  • Specifications
  • In the Box
  • Warranty

  • Antlia 3nm Narrowband H-alpha Pro Highspeed Filter - f/2.6 to f/3.6

    The Antlia 3nm Narrowband H-alpha Pro Highspeed Filter is the H-alpha filter of Antlia's 3nm Pro Highspeed series, optimized for telescopes between f/2.6 and f/3.6. Its 3nm bandpass has its center wavelength pre-shifted by 1.2nm toward the red, to 657.5nm, to compensate for the blue shift of a fast light cone. Peak transmission is 90% and out-of-band blocking is OD5 or better across 300-1000nm. On these telescopes it gives significantly better signal-to-noise ratio than the standard 3nm Pro.

    Pre-Shifted for f/2.6-f/3.6 Optics: A 657.5nm Center Wavelength

    Interference filters experience a wavelength shift toward blue when used in fast optical systems. The light path of a telescope is a cone, and an interference filter's center wavelength shifts toward the blue as the angle of incidence grows; the shift also depends on the substrate's refractive index and thickness. Antlia's simulation shows that at f/2.6 the angle of incidence is 10° and the band shifts 2.2nm toward shorter wavelengths. The Highspeed filter is therefore pre-shifted 1.2nm toward the red, to 657.5nm, so the 656.3nm H-alpha line stays well inside the band on fast telescopes.

    Between f/2.6 and f/3.6, these Highspeed filters give much stronger and more contrasted images than the standard Pro version, and they can be used in that range with minimal loss of signal.

    3nm Bandpass with 90% Peak Transmission

    The 3nm Full Width at Half Maximum (FWHM) passes a narrow band around the H-alpha line, so less moonlight and artificial light reach the camera with it. Targets include emission nebulae, planetary nebulae, Wolf-Rayet nebulae and supernova remnants; the North America Nebula (NGC 7000) and the Rosette (NGC 2237) are strong H-alpha emitters.

    Peak transmission is 90%. The filter can be used in light-polluted areas and at dark sites, and it extends imaging time when the moon is up.

    OD5 (0.001%) Blocking and Single-Substrate Design for Halo Suppression

    Out-of-band blocking is OD5 or better (no more than 0.001% gets through) from 300 to 1000nm, which delivers an excellent signal-to-noise ratio and an effective cut-off that minimizes interference from other wavelengths. The sharp cut-off of the 3nm Pro series is designed to minimize halos around bright stars.

    Further enhancing image clarity, the filter is constructed from a single, non-glued substrate of optical glass. The single substrate eliminates internal reflections. Unmounted Highspeed filters are edge blackened, which eliminates internal reflections from stray light.

    Lambda/4 Wavefront and <30 Arcsecond Parallelism

    The transmitted wavefront is Lambda/4 or better: the filter adds no more than a quarter of a wavelength of wavefront error.

    Parallelism between the faces is less than 30 arcseconds and surface quality is 60/40 scratch/dig per MIL-O-13830. The filter is 2mm thick in the 1.25", 2", 31mm and 36mm sizes and 3mm in the 50mm size. Its optical reliability reduces post-processing.

    Highspeed, Standard 3nm Pro or 4.5nm EDGE

    Antlia matches its series to the focal ratio:

    • 3nm Pro Highspeed (This Filter): For f/2.6 to f/3.6. Its center wavelength is pre-shifted to compensate for the blue shift in this range.
    • Standard 3nm Pro: Antlia highly recommends it for optics slower than f/3.6.
    • 4.5nm EDGE: The recommended choice for optics faster than f/2.6.

  • How will the Antlia 3nm Highspeed filter perform on my f/8 SCT?

    Use the standard filter instead. For optics slower than f/3.6, Antlia highly recommends the standard 3nm Pro filter, which is not pre-shifted. At f/8 the blue shift is small, so the Highspeed band would sit 1.2nm to the red of the H-alpha line.

    I'm imaging the Horsehead Nebula (Barnard 33) with an f/2.8 system. Is the Antlia 3nm Highspeed the right H-alpha filter?

    Yes. f/2.8 is inside the f/2.6 to f/3.6 range for the Highspeed series, where the filter gives significantly better signal-to-noise ratio than the standard 3nm Pro. The glowing hydrogen of IC 434 behind the Horsehead is H-alpha emission.

    Why is this Antlia filter's center wavelength 657.5nm instead of the H-alpha line at 656.3nm?

    It is intentional. Fast optics shift a filter's band to shorter wavelengths (blue shift); Antlia's simulation gives 2.2nm at f/2.6. Antlia applies a 1.2nm pre-shift toward the red to compensate, so the 656.3nm H-alpha line stays well inside the band on f/2.6 to f/3.6 telescopes.

    What does OD5 blocking mean for my images with the Antlia 3nm Highspeed filter?

    OD5 stands for Optical Density 5, which means the filter blocks at least 99.999% of unwanted light (transmitting only 0.001%) outside its narrow 3nm passband. This is specified from 300nm to 1000nm. This blocking delivers an excellent signal-to-noise ratio and minimizes interference from other wavelengths.

    Will I need to refocus between this Antlia 3nm Highspeed filter and my other filters?

    Two different thicknesses are specified for this filter series. The 1.25", 31mm, 36mm, and 2" sizes are 2mm +/-0.05mm thick, while the 50mm size is 3mm +/-0.05mm thick. The filters are not specified as parfocal, so check focus after a filter change.

    Does the Antlia 3nm Highspeed filter reduce halos around bright stars like Alnitak?

    The sharp cut-off of the 3nm Pro series is designed to minimize halos around bright stars, and the single, non-glued substrate eliminates internal reflections. Very bright stars such as Alnitak can still show some halo.

  • Filter Type H-alpha narrowband (3nm Pro Highspeed series)
    Recommended f-ratio f/2.6 to f/3.6
    Center Wavelength (CWL) 657.5nm (pre-shifted 1.2nm for fast optics; H-alpha line 656.3nm)
    Bandwidth (FWHM) 3nm
    Peak Transmission 90%
    Blocking >=OD5 (0.001%) @ 300-1000nm
    Substrate Optical, single / non-glued substrate
    Transmitted Wavefront Lambda/4 or better
    Parallelism < 30 arcsec
    Surface Quality 60/40 (scratch/dig) per MIL-O-13830
    Filter Thickness 2mm +/-0.05mm (1.25", 31mm, 36mm, 2"); 3mm +/-0.05mm (50mm)
    Edge Treatment Unmounted filters are edge blackened
    Filter Cell (Mounted) 1.25" (M28.5x0.6), 2" (M48x0.75), ultra-thin, black anodized
    Not Recommended For Solar imaging, night visual observation
    Safety Warning Do not look at the Sun with this filter
    Filter Size 1.25" Mounted, 31mm Unmounted, 36mm Unmounted, 2" Mounted, 50mm Unmounted (by variant)

    • Antlia 3nm H-alpha Pro Highspeed filter (selected size)

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    • Protective case

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  • Antlia 3-year warranty against delamination.