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  • Astrodon 3 nm Narrowband Filters – NII 3nm


    Filters in stock ship usually ship within 3 weeks.

    You may click the “Get an alert” button to be notified when an out of stock filter is back in stock. It is necessary to pay for back-ordered filters immediately to reserve your spot in our wait list. Often we have more orders for out of stock filters than we have incoming filters. Many Astrodon filters are perpetually out of stock for this reason.

    NII Filter, 3nm, center bandwidth 658.4 nm

    What about NII and H-a?
    This is a bit complicated. It is not well known that most H-a filters pass both H-a and NII. H-a emits at 656.3 nm and NII emits most strongly at 658.4 nm (and weakly at 653.8 nm). These are very close together spectrally. Thus, most H-a filters are wide enough (e.g. 4.5 nm bandwidth and wider) to pass both emission lines as shown for the older Astrodon 6 nm filter above. Our 3 nm H-a begins to separate both emission lines and reduces the NII contribution significantly. In this example the 3nm filter only transmits 15% at the NII 658.4 nm wavelength, whereas the H-a remains unchanged. As mentioned earlier, some objects are enriched in NII, such as planetary nebula and Wolf-Rayet bubbles. The Dumbbell Nebula, M27, is a good example. The wispy clouds in the core of M27 are dominantly NII. A tricolor narrowband image is also shown below, mapping OIII to blue, H-a to green and NII to red to produce a beautiful color image. This information provides you with a choice based upon your light pollution, desire for more detail, or simply wanting all the photons you can get out
    of your H-a filter.

    Our NII filters have a center bandwidth of 658.4 nm.


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