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Antlia 3nm Narrowband OIII Pro Highspeed Filter - f/2.6 to f/3.6
The Antlia 3nm Narrowband OIII Pro Highspeed Filter is the OIII filter of Antlia's 3nm Pro Highspeed series, optimized for telescopes between f/2.6 and f/3.6. Its center wavelength is pre-shifted 1.2nm toward the red, to 501.9nm, to compensate for the blue shift of a fast light cone around the 500.7nm OIII line. It has a 3nm FWHM, 90% peak transmission and OD5 or better blocking from 300-1000nm. On these telescopes it gives significantly better signal-to-noise ratio than the standard 3nm Pro.
Pre-Shifted 501.9nm CWL for f/2.6-f/3.6 Systems
Interference filters experience a "blue shift" in fast optical systems, where the steep light cone causes the filter's passband to shift toward shorter wavelengths. The shift grows with the angle of incidence and 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. The Highspeed filter compensates with a 1.2nm pre-shift toward the red, to 501.9nm.
Between f/2.6 and f/3.6, the Highspeed filters give much stronger and more contrasted images than the standard Pro version, with minimal loss of signal.
3nm Bandpass and 90% Peak Transmission
The 3nm band passes much less light pollution, moonlight and airglow around the OIII line than a wider band. Peak transmission is 90%.
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Target Objects: Emission nebulae, planetary nebulae, Wolf-Rayet nebulae and supernova remnants; the Dumbbell (M27) and the Veil (NGC 6960) are strong OIII emitters.
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Imaging Conditions: It can be used in light-polluted areas and at dark sites, and it extends imaging time when the moon is up.
OD5 Blocking and Single-Substrate Construction
Signal purity is maintained by blocking unwanted wavelengths to an optical density of 5 (OD5) or greater, which corresponds to transmitting only 0.001% of light across a wide range from 300nm to 1000nm. This delivers an excellent signal-to-noise ratio and minimizes interference from other wavelengths.
The filter is built on a single, non-glued substrate, which eliminates internal reflections, and unmounted versions are edge blackened against stray light. The sharp cut-off of the 3nm Pro series is designed to minimize halos around bright stars.
Lambda/4 Wavefront and Ultra-Thin Filter Cell
The transmitted wavefront is Lambda/4 or better, parallelism 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.
Mounted versions are housed in an ultra-thin, black-anodized cell with standard M28.5x0.6 (1.25") or M48x0.75 (2") threads. The ultra-thin cell minimizes vignetting by maximizing the clear aperture. The cells screw in by a male thread.
Highspeed Pro vs. Standard Pro vs. EDGE: Choosing the Right Antlia Filter
Antlia matches its series to the focal ratio:
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This 3nm Highspeed Pro Filter: For f/2.6 to f/3.6, where the pre-shift compensates for the blue shift.
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Antlia 3nm Standard Pro Filter: Antlia highly recommends it for optics slower than f/3.6.
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Antlia 4.5nm EDGE Filter: The recommended choice for optics faster than f/2.6.
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Why is the Antlia OIII Highspeed filter's wavelength 501.9nm instead of 500.7nm?
The 501.9nm center wavelength is intentionally pre-shifted by 1.2nm toward the red. Fast optical systems (f/2.6-f/3.6) cause a "blue shift" that moves a filter's passband to shorter wavelengths. The pre-shift compensates for that, so the 500.7nm OIII line stays well inside the band on f/2.6 to f/3.6 telescopes.
Can I use the Antlia 3nm OIII Highspeed filter on my f/8 telescope?
Use the standard filter instead: for optics slower than f/3.6, Antlia highly recommends the standard 3nm Pro filter. At f/8 the blue shift is small, so the Highspeed band would sit 1.2nm to the red of the OIII line.
How will the Antlia 3nm OIII Highspeed filter perform on the Veil Nebula (NGC 6960) with an f/3 telescope?
f/3 is inside the f/2.6 to f/3.6 range for the Highspeed series. The Veil has strong OIII emission, and the 3nm bandpass passes it with much less of the surrounding sky background.
What happens if I use this Antlia Highspeed filter with an f/2 system?
f/2 is faster than the range this filter is optimized for, and its larger blue shift goes beyond what the 1.2nm pre-shift was set for. For optics faster than f/2.6, the 4.5nm EDGE filters are the recommended choice.
Does the 3nm FWHM on the Antlia OIII Highspeed filter reduce halos?
While a narrow bandpass increases contrast, halo reduction is primarily achieved through other design features. The 3nm Pro series has a sharp cut-off profile to minimize halos. The single, non-glued substrate and the blackened edges of unmounted versions eliminate internal reflections.
Can I use the Antlia 3nm OIII Highspeed filter for visual observation?
No. Night visual observation and solar imaging are listed under Not Recommended. Do not look at the Sun with this filter.
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| Filter Type |
OIII Narrowband (3nm Pro Highspeed Series) |
| Recommended F-Ratio |
f/2.6 to f/3.6 |
| Central Wavelength (CWL) |
501.9nm (pre-shifted 1.2nm for fast optics; OIII line 500.7nm) |
| FWHM |
3nm |
| Peak Transmission |
90% |
| Blocking |
≥OD5 (0.001%) @ 300-1000nm |
| Substrate |
Optical, single / non-glued |
| 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") |
| Filter Thickness (50mm) |
3mm ±0.05mm |
| Edge Treatment |
Unmounted filters are edge blackened |
| Filter Cell (Mounted) |
1.25" (M28.5x0.6), 2" (M48x0.75), ultra-thin, black anodized, laser engraved |
| 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) |
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Antlia 3nm OIII Pro Highspeed filter (selected size)
× 1
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Antlia 3-year warranty against delamination.
