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The next filter to complement your LRGBH-a set is an oxygen filter. OIII (“ohthree”) emits light near 500 nm and is a blue-green- or teal-colored filter. Many of my images of planetary nebula and supernova remnants are taken only with H-a and OIII filters. They show great structural detail, but have natural colors, looking like an RGB image.
Astrodon OIII filters have a center bandwidth of 500.1 nm.
Astrodon Narrowband Astrophotography Filters for astrophotography 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 Astrophotography Filters are renowned for minimizing halos around bright stars – even for long exposures of 30-45 minutes which are typical of narrowband imaging in astrophotography.
Lastly, Astrodon Narrowband filters are coated to the edge of the part and are edge blackened. These features are critical to minimize stray light for a filter that blocks most light except for the narrow bandpass.
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 expensive to manufacture. Compared to the much less expensive 7- 8.5 nm filters on the market, our filters allow you to 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. The other brand 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 Astrodon narrowband filters.
For the FAQ guide, click here.
For the narrowband general knowledge presentation, click here.
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