Antlia 3.5nm Narrowband Sulfur II (SII) Imaging Filter - 2" Mounted

The Antlia Sulfur II (SII) 3.5nm filter is suitable for imaging of SII emissions from nebulas, planetary nebulas and supernova remnants. The 3.5nm bandwidth delivers a high transmission at a center wavelength of 671.6nm. The extreme narrowness in bandwidth enables astro-imaging from heavily light polluted locations and delivers improved contrast at darker sites. The filter effectively suppresses interference from other wavelengths, especially artificial mercury and sodium lamps.

Antlia narrowband filters are designed to bring out the faintest features in nebulosity by reducing the unwanted background frequencies – the narrower the filter, the better. Antlia's SII filter is designed to deliver 90% transmission at the 671.6nm line. The out-of-band blocking specification is rated OD3 (0.1%) which delivers an excellent signal-to-noise ratio and effective cut-off rate to minimize interference from other wavelengths.

A sharp cut-off rate is a very important performance index since it is designed to sharply attenuate off-band wavelengths. The result is that the Antlia SII filter delivers excellent contrast with extremely dark backgrounds whilst delivering a high transmission of the SII signal. The sharp cut-off also minimizes the effect of halos around bright stars.

In the production process, Antlia uses very strict quality control standards. Each filter is individually tested and scanned to ensure that the product meets their high-performance parameters. Their exacting attention to tolerances requires each substrate to have a uniform thickness that achieves no more +/-0.05mm deviation from specification.

Application and Performance:

• Ultra-narrow 3.5 nm bandwidths, designed for astronomy imaging in both light polluted and dark sites.
• Suitable for imaging of SII emission in nebulas, planetary nebulas and supernova remnants.
• With the Ha, SII, OIII set of filters (Ha and OIII sold separately), you are able to process your images to achieve the impressive Hubble color palette.
• High transmission of typically 90% and sharp cut-off delivers an excellent boost in contrast for SII emitting objects.
• All Antlia Narrowband filters are edge blackened to minimize interference from stray light.
• This filter is not suited to deep sky objects that do not contain SII emissions. It can be used to image SII regions in galaxies and such images can be combined into LRGB images to better highlight the SII emitting regions of galaxies.

Technical Data:

• Schott optical substrate
• 2” mounted (2mm thickness +/-0.05mm). Additional sizes available separately
• Surface Quality: 60/40 (Refer to MIL-O-13830)
• 2 sides fine-optically polished to ensure accurate 1/4 wavefront
• 30 arcsec parallelism
• Center-Wavelength of Antlia SII 3.5nm filter: 671.6nm
• SII 671.6nm T>90%, 90% transmission at SII line 671.6nm
• OD3 (0.1%) @ 300-1000nm
• 2 sides Multi-layers anti-reflection coating
• Single / Non-glued substrate

Filter Ring:

• 2” Mounted (M48*0.75 thread)
• Ultra-thin filter cell to minimize vignetting by maximizing possible clear aperture
• Black Anodized Finish
• Laser Engraving, No Fading

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.