Orion 1.25" Extra-Narrowband Tri-color CCD Filter Set

The Orion 1.25" Extra-Narrowband Tri-color CCD Filter Set consists of Orion Hydrogen-alpha (#5587), Oxygen-III (#5578) and Sulfur-II (#5579) extra-narrowband imaging filters (1.25"). These specialized "line" filters transmit only the specific wavelengths of light important in emission nebulas, while blocking out all the rest. The filters are designed for use with the Orion StarShoot Deep Space CCD Monochrome Imager II (#52083) and Manual 5-Filter Wheel (#5520), or with similar cameras.

The H-alpha filter has a transmission of 90% at the hydrogen-alpha line of 656.3nm and a full width at half-maximum (FWHM) bandpass of 7nm. The O-III filter passes light at the 500.7nm wavelength (the Oxygen-III line) with very high 90% transmission and a bandpass of 7nm. And the S-II filter passes light at the 672.4nm wavelength (the Sulfur-II line in the deep red end of the visual spectrum) with 90% transmission and a bandpass also of 7nm. Images taken with extra-narrowband filters typically look different from those acquired using standard "true color" (RGB) methods.

Rather than rendering an image in its "natural" color, the extra-narrowband filters provide a visual representation of the elemental makeup of a nebula, highlighting with assigned colors the areas where the light derives predominantly from either S-II, O-III, or H-alpha ions. This is the approach used by astronomers for many of the nebula pictures taken with the Hubble Space Telescope. The extra-narrowband tri-color images, while beautiful, also reveal much about the chemical composition of the nebula and its various features.

These 1.25" filters are made from high-grade glass and feature vacuum-deposited dichroic interference coatings and antireflection coatings. Each filter is held in an anodized aluminum cell that is threaded to fit a standard CCD camera 1.25" nosepiece or the Orion Multiple Filter Wheel. All three filters are parfocal with each other, so refocusing is not needed when switching between filters in the set. It includes a protective plastic case for each filter.