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 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.

Technical Specifications:

Basic Substrate: Schott optical substrate

Filter Thickness：2mm+/-0.05mm for 2'' mounted

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

Single / Non-glued substrate