Antlia 3nm SII Pro Series Filter - 1.25" - SII-PRO-3NM-125

This very narrowband 3 nm SII filter from Antlia is part of their Pro series and comes in a 1.25" threaded filter cell that is designed to be screwed on to the 1.25" receptacle of your astrophotography accessory, including a 1.25" filter wheel.

Photo shows the 2" version of this filter.

Antlia 3nm Pro Series Sulfur II Filter - 1.25" Mounted

This Antlia SII Pro narrowband filter optimizes the FWHM (full width half maximum) to a 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 88% 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>88% 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.

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：2mm+/-0.05mm for 1.25'' mounted

Filter Cell:  M28.5*0.6mm

FWHM (Full width at half maximum): 3nm

CWL (Central Wavelength): 671.6nm

Peak Transmission: ＞88%

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