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Astrodon 3 nm H-Alpha Narrowband Filter - 31 mm Unthreaded Insert - HA3-31R

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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
  • 31 mm unthreaded
  • >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 Narrowband Filters

Highly favored among narrowband filters, hydrogen-alpha filters for 656 nm are deep red in color. As it is the most common element in the universe, hydrogen is present in emission nebula such as the North American and the Pelican, planetary nebula such as the Dumbbell and Ring, Wolf-Rayet objects like Cresecent and Thor's Helmet, as well as supernova remnants like the Veil nebula. While many imagers are content to dsiplay a simple black and white h-alpha image of an object, most imagers will want to combine their h-alpha data with their red RGB data in order to augment structural detail while preserving a "natural" appearance. For this reason, h-alpha filters make a perfect initial narrowband extension of your LRGB filters.

Astrodon Narrowband Filters - Additional Information

Astrodon Narrowband filters set a new standard for imaging and research performance and durability. These filters enhance contrast in emission line objects via narrow 5 nm and 3 nm bandwidths. With a transmittance guaranteed to be above 90% at the emission wavelength, these filters offers the highest signal available. This guarantee combined with a spectrally narrow bandwidth ensures maximum contrast. As a matter of fact, the latest narrowband filters from Astrodon typically achieve a transmittance of between 95 and 98%. Even when taking exposures common to narrowband astrophotography, typically 30-45 minutes in length, these Astrodon Narrowband filters still have the ability to keep halos around bright stars at a minimum, a feature for which these filters are renowned. Finally, these filters are edge-blackened with hard-oxide coatings from edge to edge to eliminate the chance that an uncoated border will cause light leakage. This is critical to keeping stray light to a minimum for a filter that blocks all light save for the narrow bandpass.

The enhanced contrast these Astrodon Narrowband filters provide is their most distinguishing trait. With improved contrast, faint detail in emission line objects like planetary nebulae and supernova remnants becomes more apparent. This effect is even more pronounced with narrower bandwidth filters. With a filter that's spectrally narrower, however, the difficult part is maintaining a constant signal (% transmission at the emission line). This is why Astrodon's >90%T guarantee is so important as it provides assurance that you'll be able to take advantage of the upgrade in contrast these narrow bandwidth filters offer.