Notice:  As of 9/23/2025 New production has been started.  We have had some filter yeild from the intial testing runs and those filter are available for purchase now.   Please monitor our website for upcoming notices of availability dates and the ability to place pre-orders.

Status of the filter sizes are as follows:

SII 5nm - 1.25" mounted - release date TBD (check back soon)
SII 5nm - 36mm round unmounted - release date TBD (check back soon)
SII 5nm - 50mm round unmounted - release date TBD (check back soon)

The following filters came from our recent setup run and meet all specifications perfectly

SII 5nm - 50mm square unmounted - 5 in stock full release date TBD (check back soon)

All purchases will be confirmed with telephone calls to the customer before completing the transaction.

CXB (formerly Astrodon) 5nm Narrowband SII Filter (Sulfur II)

The use of our narrowband filters expands the usefulness of your imaging system by allowing you to work during the times that the moon floods the sky and to image from light poluted areas as well.  Narrowband images give a distinct Hubble Space Telescope look.  You can also supplement your LRGB images with narrowband data to enhance subtle features. Maximise your imaging equipment by using it more than one weekend a month.

CXB (formerly Astrodon) SII filters have a center wavelength of 671.6nm

Vastly Superior Construction: CXB (formerly Astrodon) filters are made using vastly superior coating technology to nearly all other brands.  They are made in the USA using export controlled technology that no other nation posesses. Anyone can design a good filter but it is how they are made that counts!  That special "how they are made" happens only in the USA and is the reason why our filters are so good.

Modern USA Coating technology controls the deposition of thousands of layers in the filter design, measuring and correcting for the errors in real time.  As each layer is deposited,  the partially constructed filter is optically measured and the remaining layers are re-computed to keep the filter performance on target.  This process essentially makes perfect coatings.   No other country has this technology, it is exclusive to the United States. 

In addition to absolutely precise control of layer deposition our technology produces coatings that are nearly 100% compacted with no voids or porosity.   Old style evaoporated coatings absorb water vapor into the coating which changes the over-all index of refaction and the resulting performance of the filter.  As the humidity changes, so does the optical response of the filter.  For narrowband filters this is a disaster.  Our nearly 100% dense filters are immune to this critical flaw. 

Becasuse our filters are impervious to water penetration they will never "delaminate" like the old style construction of most astronomy filters.  They are hard and can be cleaned without fear os destroying them.   Our coatings have an expected lifetime of more than 100 years. 

Signal to noise: The ratio of the light passed by a filters transmission band (desired) to the light passed by the blocking areas (undesirable) is the signal to noise ratio.  The higher the signal to noise, the faster you will accumulate "good data" for your images.  Good filters not only have high transmission values for the in-band portions but they also have high blocking values for the parts of the spectrum we don't want to accumulate.  Not only do our filters have extremely good in-band transmission, they have insanely good out-of-band blocking.  We've measured our competators filters and our blocking is the best on the market.  CXB (formerly Astrodon) filters deliver the highest signal to noise ratio performance on the market.

Our standard out-of-band blocking is Optical Density 5, or only .001% transmission / leakage.  Most of our cempetators struggle to obtain blocking of OD 2, or 1% leakage (we've scanned their filters, we know).  So, ask yourself, would you rather have a system that gives a signal to noise ratio of 99-to-1 or 99,000-to-1?

If you want to make the best images, you need the best tools.  Step up to the best, step up to CXB.

How to Clean your Filter

How To use a Narrowband filterMore narrowband filters

https://youtu.be/t5NAIbV1l8o

Filters in stock ship usually ship within 3 days.

Bring Out The Faint Structures In Nebulae

CXB (formerly Astrodon) Narrowband filters set a new bar of performance and durability for imaging and research. We offer 5 nm and ultra-narrow 3 nm bandwidths.

CXB (formerly Astrodon) Narrowband filters set a new bar of performance and durability for imaging and research. The narrow 5 and 3 nm bandwidths enhance contrast of emission targets by lowering your background signal. The guaranteed >90% transmittance at the emission wavelength provides you with the highest signal available. This guaranty is expensive to manufacture for such spectrally narrow filters, but it assures you in writing on each filter box that you will get what you paid for. These two factors combine to provide you with the highest contrast available. Our latest narrowband filters are typically achieving >95-98% transmittance. Astrodon Narrowband filters are renowned for minimizing halos around bright stars, even for long exposures of 30-45 minutes typical of narrowband imaging in astrophotography. Lastly, Astrodon Narrowband filters are coated to the edge of the part and are edge blackened. This is critical to minimize stray light for a filter that blocks most light except for the narrow bandpass.

CXB (formerly Astrodon) Narrowband filters for imaging are all about contrast. What do we mean by this? Contrast brings out faint features by reducing the background - the narrower the filter, the better. The problem is keeping the signal (%T at the emission line) constant as the filter becomes spectrally narrower. This is why our >90%T guarantee is so important, even though it becomes very costly to manufacture. But, this assures you that you can take advantage of the improved contrast with our narrower filters compared to the much less expensive 7- 8.5 nm filters on the market. You can see the increase in contrast in the sequence of equal-exposure images of the Crescent Nebula (NGC 6888) taken on the same system and on the same night. As the bandwidth becomes narrower, the nebula "pops" out of the background, as does the faint surrounding nebulosity. Actually, the >90%T is a legacy specification, since new production technologies employed over the past 3-4 years routinely produces 97-98%T at the emission wavelengths.

Random tests of a competitor's low-cost 7 nm H-a filter showed %T values ranging from 86% down to 71%. Random selection of 5 nm Astrodon filters measured %T values at the H-a emission wavelength of 93, 98, 97 and 98%. You will never know that you are using their 71% filter compared to a 97% Astrodon filter because they do not guarantee this important performance parameter. They recently came out with a 3.5 nm H-a narrowband filter and those results are even worse, ranging from 3-70% at the emission wavelength. Similarly, analysis of different 2016 lots of Astrodon 3 nm H-a filters measured 97, 97, 97 and 96%T. Yes, our filters are more expensive, but you always know what you are getting with Astrodon Narrowband filters - the best performance in the market - guaranteed. Our recent blueshift data show that Astrodon 3 and 5 nm filters can be used with nearly all systems as fast as f/3.5 with virtually no loss in emission signal, so you do not need to buy custom "upshifted" filters if you have both fast and slow systems.

Step up to the quality and performance of CXB (formerly Astrodon) narrowband filters.