Antlia 3nm Narrowband Sulfur II (SII) Pro Imaging Filter - 2" Mounted
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IMPORTANT: Please read this important note below before buying Antlia narrowband filters. No returns will be accepted for Antlia narrowband filters exhibiting halos around bright stars as disclosed below.
Please note that some users may see halos around bright stars in images made with this filter. Such halos have been observed with filters from other leading manufacturers and in the previous generation of Antlia narrowband filters as well. These halos can be caused and/or made worse by other optical accessories in the imaging train, their relative positions, telescope design/optics, camera, software, or a combination thereof. In general, OIII filters seem to have a higher propensity to show halos compared to H-alpha or S-II filters, but in rare cases the latter filters can also exhibit faint halos around bright stars.
Antlia has made great strides in their coatings to minimize haloing of bright stars, but you may still observe this effect to some degree. See the sample OIII image below of Alnitak (magnitude 1.74) and IC434 in Orion (SkyRover 155mm Apo, ZWO 6200MM-P Camera, 20 min exposure) provided by Antlia. In most cases, haloing will not affect your image unless you have very bright stars in the field of view.
Please note we are unable to accept returns of any Antlia narrowband filters if you do observe this haloing effect in your images.
If you must ensure there are no detectable halos in your images, you may want to consider Astrodon or Chroma narrowband filters instead. These filters, however, cost two to three times as much as Antlia 3nm filters do. Antlia is being honest and upfront. They are the ones telling us about these halos, that their filters are great for the money but still not as good as Astrodon/Chroma, and pointing out that with this full disclosure, they will not accept returns. They are leaving it up to the customer to decide if this is good enough for them or not. We believe that for most imaging applications, Antlia filters continue to offer excellent value for astrophotographers and these continue to be among our top sellers.
Product Details
The Antlia Sulfur II (SII) 3.0nm filter is suitable for imaging of SII emissions from nebulas, planetary nebulas and supernova remnants. The 3.0nm 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 3.0 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 3.0nm 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 (M48x0.75 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.
Useful Resources
Filter Cell Specifications
D = Filter Cell Diameter = 50.3mm / 2.0"
T = Total Filter Height = 7.3mm / 0.28"
C = Filter Cell Height (Excluding Male Thread) = 4.9mm / 0.19"
M = Male Thread Length = 2.5mm / 0.09"
F = USABLE Female Filter Thread Length = not threaded
S = Glass Substrate Thickness = 2mm / 0.07"
CA = Clear Aperture = 45mm / 1.77"
Other Information
- Country of Manufacture: China
