| This 1.25" Orion Extra Narrowband Hydrogen-alpha imaging filter lets you take high-contrast CCD images of emission nebulas in full moonlight or in extreme light pollution. Designed exclusively for deep-sky imaging of emission nebulas with CCD cameras, this high-performance Orion filter transmits 90 percent of the light at the hydrogen-alpha emission line at 6563 Ångstroms.
The Orion Extra Narrowband filter has a very narrow 7nm FWHM (full width at half-maximum) passband that lets through only the Hydrogen-alpha light emitted by nebulas. The filter blocks out all other light, including moonlight and artificial light pollution (city streetlights and parking lot lights). It also blocks infrared (IR) light. The result is a dramatic boost in contrast, revealing subtle nebular emission details that are usually washed out by contrast-killing broadband light. Stars come out tight and sharp. Note: This filter should NOT be used for daytime Hydrogen-alpha solar observation. Immediate and irreversible eyesight damage can occur if used to observe the Sun.
This Orion filter is also ideal for capturing luminance data for LRGB color imaging of hydrogen-alpha emission nebulas with monochrome CCD imagers, such as the Orion StarShoot Deep Space Monochrome Imager II. When the monochromatic H-alpha image is combined with the exposures taken through red, green, and blue filters, the resulting color image teems with fine details that are “missing in action" in a standard color shot.
In addition to monochrome images of H-alpha emission features using this filter, and the extra details to be gained in true color imaging by combining H-alpha with RGB images as mentioned above, many people use a combination of H-alpha, Sulfur II, and Oxygen III filters for tri-color CCD imaging, rather than the traditional RGB filters. Images taken with extra-narrowband filters typically look much different from those acquired using standard “true color" (red, green, blue) methods.
Rather than rendering an image in its natural color, tri-color imaging with extra-narrowband filters provide a visual representation of the elemental makeup of a nebula, with the different colors highlighting the areas where the light derives predominantly from either Sulfur II, Oxygen III, or Hydrogen-alpha emissions. This is the approach used by astronomers for many of the nebula pictures taken with the Hubble Space Telescope. It’s a technique that allows amateur astrophotographers to emulate the amazing false-color Hubble Space Telescope images, such as the famous “Pillars of Creation." The extra-narrowband “false color" images, while beautiful in their own right, also reveal much about the chemical composition of the nebula and its various features.
The Orion Extra Narrowband Hydrogen-alpha imaging filter is made from precision-polished high-grade optical glass with multiple-layer vacuum-deposited dichroic interference coatings and antireflection coatings. The filter is supplied in a 1.25" cell that threads into the 1.25" nosepiece of a CCD camera or into the Orion Multiple Filter Wheel, as well as any color filter wheel that accepts standard 1.25" filters. The filter is supplied in a foam-fitted hard plastic protective case. All three of the Orion Extra Narrowband filters (Hydrogen-alpha, Sulfur II, and Oxygen III) are parfocal, eliminating the need to refocus when switching between them during imaging.
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