Astronomik Oxygen-III (OIII) Visual Filter (2")

Astronomik Oxygen-III (OIII) Visual Filter (2")

Due to high demand and global product shortages due to the pandemic, please call for availability.

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 the 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 bee seen or not!

The optimal aperture ratio for the use of the filter is f/3 to f/15 with apertures of more than 6" (150mm). Transmission losses and chromatic distortions, which arise with other filters, occur with Astronomik OIII filters only when extremely bright aperture ratios of f/3 and more come into play. Thus, the Astronomik OIII filters 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" (150mm). Many experienced deep-sky observers with apertures of more than 10" (250mm) 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 telescope without the filter in place.

This filter is not for solar observation.

Price does not include shipping from Germany, which is separate from the possible free shipping from us to you. You will be notified of these shipping charges prior to payment being taken.


  • Transmission of nearly 100% of both OIII lines
  • Complete blocking of all other disturbing wavelengths
  • The ideal filter for telescopes 10 " (25cm) and larger
  • Main use: planetary nebulae & super nova remnants
  • parfocal with all Astronomik filters
  • Diffraction limited, the filter will not reduce the optical performance of your telescope!
  • Thickness: 1mm
  • Not sensitive to moisture, scratch resistant, non-aging
  • Excellent carrier material - substrate is optically polished. The optical performance (resolution & contrast) of your telescope is not reduced in any way by the filter.
  • High quality storage box
  • Made in Germany