Notice:  As of 10/16/2025 New production has been started and releases are scheduled over the next 12 month period.  If the filter shows available for purchse and you can add it to your shopping cart it will be delivered to you at the next release date. If you have questions, call Cary at 916-628-8673.

Status of the filter sizes are as follows:

OIII 3nm - 1.25" mounted - First release - 11/14/25
OIII 3nm - 36mm round unmounted - First release - 11/14/25
OIII 3nm - 50mm round unmounted - First release - 11/14/25
OIII 3nm - 50mm square unmounted - First release - 11/14/25
OIII 3nm - 65mm square unmounted - 5 available now.

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

Future release dates are:

CXB (formerly Astrodon) 3 nm Narrowband OIII Filter (Oxygen III)

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) OIII filters have a center wavelength of 500.1 nm.

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