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Astrodon 3 nm NII Narrowband Filter - 1.25" Threaded Cell - NII3-27R

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SKU: ASD-NII3-27R

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

Astrodon Narrowband filters enhance emission line object contrast through their narrow 5 nm and 3 nm bandwidths, setting a new standard for imaging and research performance and reliability. With a guaranteed transmittance of more than 90% at the emission wavelength providing the highest available signal, combined with such spectrally narrow bandwidth filters, imagers can be confident of attaining maximum contrast. Astrodon's latest narrowband filters, as a matter of fact, typically achieve between 95% and 98% transmittance. Acclaimed for their ability to reduce halos around bright stars, Astrodon Narrowband filters are still able to accomplish this even for long 30 to 45 minute exposures common to narrowband astrophotography. Finally, these edge blackened Astrodon Narrowband filters contain hard-oxide coatings to the perimeter to eliminate any chance of light leaking due to an uncoated border. For a filter that blocks most light save for the narrow bandpass, this becomes crucial to maintaining as low a level of stray light as possible.

With Astrodon Narrowband filters, it's all about the enhanced contrast. The better the contrast, the more the fainter characteristics of celestial objects are highlighted. This improves with filters that have narrower bandwidths. However, maintaining a constant signal (%T at the emission line) as the filter gets spectrally narrower can be difficult. This is what makes Astrodon's >90%T guarantee so critical as it assures that you'll be able to benefit from the enhanced contrast provided by narrower filters.