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Astrodon 3 nm NII Narrowband Filter - 49.7 mm Round Unmounted - NII3-50R

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SKU: ASD-NII3-50R

About Astrodon Narrowband Filters

Astrodon filters are high performing, durable filters that provide significant aid for astrophotography and research pursuits. Each filter is constructed using a highly innovative process with a single high quality 3 mm thick fused silica substrate and full hard oxide sputtered coatings. With these Astrodon Narrowband filters, imagers can count on consistently high performance, as well as a more narrow spectrum compared to most other filters for superb contrast and the ability to view the faintest nebula detail. Astrodon guarantees >90%T performance at the emission line.

Astrodon 3 nm Narrowband Filter Highlights

  • Guaranteed 90%+ maximum transmission for the highest achievable performance
  • 3 nm bandwidth
  • >OD 4 (0.01% transmission) out-of-band blocking
  • Clear 1/4 wave substrates feature hard-oxide coatings to the edge, removing light leakage from uncoated rims
  • Edge blackened to reduce reflections
  • Parfocal with all other filters made by Astrodon


Astrodon 3 nm H-Alpha & NII Narrowband Filters

It is not often recognized that most H-Alpha filters pass H-α as well as NII. H-α emits at 656.3 nm while NII emits strongest at 658.4 nm (and weakest at 653.8 nm). Since these are so close to one another on the spectrum, most H-Alpha filters are wide enough (e.g. 4.5 nm bandwidth minimum) to allow both emission lines to pass through. Astrodon's 3 nm H-α filter starts to separate both emission lines, considerably reducing NII input. In this case, the 3 nm H-Alpha filter transmits only 15% of the 658.4 nm NII wavelength, while the H-α wavelength remains constant. Some objects, such as planetary nebula and Wolf-Rayet bubbles, are enhanced in NII. For example, the wispy clouds in the core of the M27 Dumbbell Nebula are predominantly NII. A tricolor narrowband image will show OIII maps to blue, H-α to green, and NII to red to produce a magnificent color image. This will allow imagers to make an informed decision based on current light pollution conditions, desire for more detail, or simply wanting to get all possible photons from their H-Alpha filters.

Astrodon Narrowband Filters - Additional Information

Setting a new standard for imaging and research performance and durability, Astrodon narrow 5 nm and 3 nm bandwidth filters reduce background noise to enable enhanced contrast of emission objects. Transmittance is guaranteed to be above 90% at the emission wavelength for the highest signal available. The combination of this guarantee and filters with such spectrally narrow bandwidth assures the highest contrast possible. In fact, Astrodon's latest narrowband filters are known to attain 95-98% transmittance. Even when capturing extended 30-45 minute exposures typical of narrowband astrophotography, Astrodon Narrowband filters are still able to minimize halos around bright stars, a skill these filters are known for. Lastly, these Narrowband filters from Astrodon are edge-blackened and feature coatings to the edge of the part. This is integral to keeping the stray light as low as possible for a filter that blocks most light not in the narrow bandpass.

The most important aspect of Astrodon Narrowband filters is the improved contrast they provide. As contrast improves, faint detail of emission line objects such as planetary nebulae and remnants of supernovae is further enhanced. With filters that have narrower bandwidths, this effect is even more pronounced. The downside is that keeping a constant signal (% transmission at the emission line) can be an issue with spectrally narrower filters. This is where Astrodon's >90%T guarantee comes in. With this guarantee, you'll know that you can depend on being able to take advantage of the improved contrast offered by filters with narrower bandwidths.

Main image may not depict the exact filter you will receive.