This 1.25” filter has a moderately wide 560 Ångstrom passband for visual use on emission nebulas in slight to moderately light polluted areas. It typically has a peak transmission approaching 96% at the visually important emission lines of hydrogen-beta at 4861Å and doubly ionized oxygen at 4959Å. Transmission at the 5007Å doubly ionized oxygen line is typically approaches the somewhat lower (but still good) 88% range. While it has acceptable performance on reflection nebulas due to its moderate passband, a wider passband filter would be more useful on this type of object, as the wider passband would show more reflected starlight detail. Transmission at the photographically important ionized nitrogen and hydrogen-alpha lines near 6570Å is only fair, making this filter best suited primarily for visual use with 1.25” eyepieces, rather than any photographic use. It has very steep passband cutoff slopes that yield higher contrast than competitive filters of a similar passband width that have more gradual transition slopes. All coatings are sandwiched between two layers of glass to protect them against accidents and too-aggressive cleaning.
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