A New Bandpass Combination for Imaging: Antlia ALP-T Dual Band SII / H-beta Filter Review

Multi-narrowband filters for one-shot color cameras are rapidly becoming more popular for their light-pollution-defeating benefits and the speed of using a one-shot color camera rather than monochrome. H-alpha and OIII are the most commonly used emission lines in multi-narrowband filters, but Antlia has a noteworthy new combination: H-beta and SII!




H-alpha light – that deep red glow from hydrogen gas at a wavelength of 656 nm – has been the most widely used and best-known emission line for astronomers. But hydrogen also has a prominent optical emission at a turquoise-blue 486 nm known as H-beta. This transition in hydrogen requires more energy to drive it, so H-beta light mainly occurs near hot, young, strong UV-emitting stars. An object that emits H-beta light also emits H-alpha light but the reverse is not always true. So, some emission nebulae will have H-beta, and some will not.

With a one-shot color camera, imaging light in different parts of the spectrum can activate the red, green, and blue pixels together in one shot, saving time. H-beta light includes blue and green, and the SII band in this filter covers the red. The ALP-T filter has 5nm bandpasses.


Imaging Results

So how does this filter look on deep-sky objects? The Orion Nebula was a natural choice to try it out.


Celestron Edge HD 9.25”, ZWO ASI2600MC Pro, 53×60-sec. Credit: AstronoMolly


Because this filter passes the blue light of hydrogen, you get an almost reverse image of M42 compared to using H-alpha and OIII. The SII signal provides coverage in the red part of the spectrum where H-alpha usually dominates but H-beta is less prominent (such as in M43 in the lower left of the image above). The SII light is dim compared to hydrogen and oxygen, though, so I split the red, green, and blue channels before stretching the above image to enhance the red SII signal. That worked quite well and wasn’t difficult to achieve.

Curious to see what other nebulae would look like, I next imaged the Ghost of Jupiter Nebula.


Celestron Edge HD 9.25”, ZWO ASI2600MC Pro, 80×180-sec. (4 hours total). Credit: AstronoMolly)


Like many others, this planetary nebula doesn’t have much, if any, sulfur, but the H-beta signal is still prominent. Ordinarily, very bright nebulae like this one are difficult to process because the nebula is so much brighter than the background. Because H-beta is not as bright as the OIII in this nebula, though, this one was much easier to stretch nicely.

An important question with narrowband filter is “Are there halos?” I put this filter to the test by imaging Polaris for 30 seconds. The results were very positive.


Polaris; Celestron Edge HD 9.25”, ZWO ASI2600MC Pro, 30-sec single frame.
Left: Antlia ALP-T Dualband SII-Hb, right: Optolong L-Ultimate. Credit: AstronoMolly


Even on this second magnitude star, the image is nice and tight, performing as well as another dual-narrowband filter I have, the Optolong L-Ultimate. The two produce similar images of Polaris, as shown above, but note that the Antlia has 5nm bandpasses compared to the L-Ultimate’s 3nm.

One way to use this filter is in combination with a dual-bandpass Ha and OIII filter to create unique color palettes. Antlia provides some ideas and examples on the Orion Nebula.

H-alpha, OIII, H-beta, & SII color palette examples on M42. Credit: Antlia.



The new Antlia ALP-T Dual Band 5nm SII and Hb filter brings new possibilities to your one-shot color imaging. You can create new perspectives on familiar targets with this filter alone or combine it with an H-alpha and OIII filter to create unique color palettes. It performs very well with bright stars, showing no signs of haloing. It has been fun to use, and I look forward to more cool images!


MSRP: $350


About AstronoMolly

I got into astrophotography in July 2015 after receiving my first telescope as a gift. Much trial and error later, I now have four astrophotography rigs set up in my backyard in Dayton, OH, including one dedicated to variable star and exoplanet transit observations, and I am now also a Contributing Editor at Astronomy Magazine. I love doing STEM and astronomy outreach both in-person at public stargazes and virtually on YouTube and at astronomy club meetings and classrooms across the country. I am an AAVSO Ambassador (American Association of Variable Star Observers), an Explore Alliance Ambassador, and a panelist and broadcaster for The Astro Imaging Channel weekly YouTube show. I have a B.S. in Physics from Washington State University, and am currently pursuing my PhD in Nuclear Engineering while snuggling with my two cats, Orion and Apollo.

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