Antlia SII Pro narrowband filter optimizes the FWHM (full width half maximum) to 3nm bandpass. As the bandwidth becomes narrower, the 3nm Pro narrowband filters enhance contrast of emission targets by lowering the unwanted background signal. Antlia SII 3nm Pro filter is designed to deliver 90% transmission at the 671.6nm line which provides you with the maximum signal and well defined nebulae structures.

Conventional broader narrowband filters cause a heavy loss in transmission due to the strong (Center Wavelength (CWL)-shift. We guarantee T>90% within 1nm range of the center bandwidth,which means that the 3nm Pro narrowband filter can guarantee high transmittance for working with both long focal ratios and fast optical systems. Blue-shift data show that Antlia 3nm Pro filters can be used with nearly all systems as fast as f/3 with minimal loss in emission signal and meets the requirements of fast optics like Hyperstar and RASA.

The out of band blocking specification is rated OD5 (0.001%) which delivers an excellent SNR(signal to noise ratio) and effective cut-off rate to minimize interference from other wavelengths. Improved sharp cut-off astrophotography 3nm Pro filters are designed to minimize halos around bright stars.

When we design filters for astronomy imaging systems, we look at how they will work together with optical systems, carefully designing the blocking and band-pass parameters to achieve an optimum result. The out of band blocking rate is a very important performance index since it is designed to sharply attenuate off-band wavelengths. The result is that the Antlia SII 3nm Pro filter delivers excellent contrast with extremely dark backgrounds whilst delivering a high transmission of the SII signal. Such filters are more difficult to produce to a consistently high standard.

Each filter is individually tested and scanned to ensure that the quality meets the high- performance parameters. The end result is a filter that achieves excellent contrast but with a higher production cost. We believe the price to performance ratio compares more favorably than similar premium filters in the market.

Application and Performance:

• High transmittance and smallest bandwidth to maximize contrast
• Steep spectral profile minimizes halos around bright stars
• A single substrate to eliminate internal reflections
• Narrowband Objects: SII Emission Nebulae, Planetary, Wolf-Rayet Nebulae and Supernova Remnants
• Use in light polluted areas and dark sites
• Extend imaging time when the moon is up
• All Antlia narrowband Pro filters can be used down to F/3 with slight loss of signal
• All Antlia Narrowband filters are edge blackened to eliminate internal reflections from stray light
• Superior optical reliability reduces post image processing
• This filter is not suited to deep sky objects that do not contain SII emissions

Technical Specifications:

• Basic Substrate: Schott optical substrate
• Filter Thickness
  Measured thickness： 2mm+/-0.05mm for 1.25’’, 2’’ mounted, Dia31mm and Dia36mm unmounted
  Measured thickness： 3mm+/-0.05mm for Dia50mm unmounted
• FWHM (Full width at half maximum): 3nm
• CWL (Central Wavelength): 671.6nm
• Peak Transmission: ＞ 90% transmission at SII line 671.6nm
• Blocking: > 5 OD(0.001% out of band blocking) @ 300-1000nm
• Surface Quality: S/D (scratch/dig)= 60/40 (Refer to MIL-O-13830)
• Transmitted Wavefront: Lambda/4 or better.
• Parallelism: less than 30 arcsec
• Single / Non-glued substrate

Filter Ring:

• 1.25’’ (M28.5*0.6)， 2’’ (M48*0.75)
• Ultra-thin filter cell to minimize vignetting by maximize possible clear aperture
• Black Anodized Finish
• Laser Engraving No Fading

Sizes：

• Mounted： 1.25’’， 2’’
• Unmounted： Dia31mm， Dia36mm， Dia50mm

Not Recommended:

• Solar Observing and imaging
• Visual observation
• DO NOT LOOK AT THE SUN WITH ANTLIA FILTERS.
• Serious eye damage will result if you fail to observe the warning.