Astronomik OIII Filter - 1.25" Round Mounted

Astronomik OIII Filter - 1.25" Round Mounted
Item # AK-OIII-1
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  • This Astronomik OIII Filter is made for visual observing of gas and planetary nebulae.
  • This model is mounted in a 1.25" metal cell.
  • With a FWHM of ca. 15nm, the Astronomik OIII Visual Filter transmits at nearly 100% in the OIII line.
  • On larger telescopes (10" & over), this may very well be the filter of choice for deep-sky observing.
  • Astronomik OIII Filters are best on telescopes of at least 6" of aperture.


Astronomik 1.25" OIII Filter for Visual Use

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 bee seen or not!

The optimal aperture ratio for the use of the filter is 1:3 to 1:15 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 1:3 and more come into play. 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" (150mm). Smaller instruments do not gather enough light for meaningful and satisfying astronomical work. However, please note: 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 regular telescope.

Astronomik 1.25" OIII Filter for Visual Use Features

  • Transmission of nearly 100% of both OIII lines
  • Complete blocking of all disturbing wavelength coverages
  • The ideal filter for telescopes 10 " (25cm) and larger
  • Main operational use: Planetary nebulas & super nova remnants
  • No moisture-sensitivity, no aging, and totally scratch-proof
  • Excellent carrier material - substrate is optically polished. The optical performance (resolution & contrast) of your telescope is not reduced in any way by the filter.
  • Parfocal with other Astronomik filters
  • Glass thickness: 1mm
  • Completely resistant against high humidity, scratches and aging effects
  • Diffraction limited, the filter will not reduce the optical performance of your telescope!
  • Astronomik filters are delivered in a high-quality, long lasting, filter box
Additional Information

Additional Information

Manufacturer Astronomik
Type of Filter Oxygen III
Filter Usage Imaging, Visual
Single or Set? Single Filter
Filter Size 1.25"
Filter Shape Round
Filter Mounted? Mounted
Warranty 10 Year Warranty
Peak Transmission Nearly 100% for all OIII lines
Included Items

Included Items

  • Astronomik 15nm OIII Filter for Visual Work - 1.25"
  • Protective Plastic Case
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