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Astronomik OIII Visual Filter - 2" Round Mounted - OIII-2

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SKU: ASF-OIII-2

Astronomik OIII Visual Filter - 2" Round Mounted


  • This Astronomik OIII Filter is mounted in a round 2" cell and is best-suited for visual observation of gas and planetary nebulae
  • This filter contains a transmission close to 100% in the OIII line
  • FWHM bandwidth of roughly 15 nm
  • Coatings help shield this filter from the impacts of scratching, aging, and humidity
  • The Astronomik 2" OIII Visual Filter is diffraction limited for maintaining the optical performance of your telescope
  • Works best on telescopes with an aperture of at least 6"
  • German-made for superb quality optics!


More About the Astronomik 2" OIII Visual Filter


From the beginning, Astronomik's OIII visual filter has been expressly designed for gaseous and planetary nebulae observation. The severely narrow pass band of the two OIII lines produces a significant contrast gain to these lines even in the most ideal seeing environment. This filter will frequently make the difference between being able to see faint supernova remnants and planetary nebulae and missing them altogether! Therefore Astronomik OIII filters, in general terms, broaden the view of scattered objects in the entire visual field of view, and are not constricted to only the center of the eyepiece.

Because a sufficient amount of light needs to be available to employ the OIII filter, it is advantageous to use this filter with telescopes that have apertures of 6" (150 mm) or more. Instruments with smaller apertures will not capture enough light for any worthwhile astronomical output. On the other hand, many experienced deep sky observers prefer using the OIII filter in lieu of the more versatile UHC filter with apertures above 10" (250 mm). The exceptional optical quality of the Astronomik OIII filter substrate will allow you to view the same razor sharp stars you would see through the telescope you normally use.

The Astronomik OIII Visual Filter features close to 100% transmission of both OIII lines. The substrate is optically polished providing superb carrier material. As with all filters from Astronomik, this filter is parfocal with all other Astronomik filters. Includes a durable, high-quality plastic storage box.

Transmission Specifications


  • Over 99% transmission for either OIII line
  • Obstructs undesired wavelengths in other areas of the visible spectrum