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Astronomik OIII Visual Filter - 1.25" Round Mounted - OIII-1

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SKU: ASF-OIII-1

Astronomik OIII Visual Filter - 1.25" Round Mounted


  • The Astronomik 1.25" Round Mounted OIII Visual Filter is made for visual observing of gas and planetary nebulae
  • This filter has a Transmission of nearly 100% in the OIII line
  • The Astronomik OIII Visual Filter has a FWHM bandwidth of approx. 15 nm
  • Coatings protect amazingly well against scratching, aging, and humidity
  • Diffraction limited, the filter will not reduce the optical performance of your telescope
  • The Astronomik OIII filter is best used on telescopes with at least 6" aperture
  • Made in Germany, a country renowned for their optical quality!


More About the Astronomik 1.25" OIII Visual Filter


From the start, the Astronomik OIII filter has been very specifically designed for the visual observation of gaseous and planetary nebulae. The extremely narrow pass band of the two OIII lines brings a substantial contrast gain to these lines even under best observation conditions. On faint super nova remnants and faint planetary nebulae the Astronomik OIII filter will often make the difference as to whether the object can be seen or not! The Astronomik OIII filters thus can expand the view of dispersed objects, generally speaking, to the whole visual field of view of the eyepiece, and are not limited to only the center of the eyepiece.

Since enough light must be available to make use of the OIII filter it is best to use this filter with apertures of more than 6" (150 mm). Smaller instruments do not gather enough light for meaningful and satisfying astronomical work. However, please note: Many experienced Deep Sky observers, with apertures larger than 10" (250 mm), prefer using the OIII filter instead of the more versatile UHC filter. Due to the high optical quality of the Astronomik OIII filter substrate you will see the same needle-sharp stars as you would from your regular telescope.

The OIII Visual Filter from Astronomik has nearly 100% transmission of both of the OIII lines. Excellent carrier material - the substrate is optically polished. Parfocal with other Astronomik filters. Astronomik filters are delivered in a high-quality, long lasting, plastic filter box.

Transmission Specifications


  • 99+% transmission for both of the OIII lines
  • Blocks unwanted wavelengths in other parts of the visible spectrum