Astronomik OIII 6nm CCD Clip-Filter Pentax K

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Astronomik OIII 6nm CCD Clip-Filter Pentax K

The Astronomik OII-CCD Filter is perfect for imaging OIII nebulas both from places with heavy light pollution and from the best dark site you can find as well. The contrast between the background and an object emitting at 501nm is enormously increased with this filter.

This contrast boost is enabled by the high transmission of 96% of its 6nm narrow bandwidth, blocking all other unwanted bandwidths, and if you wanted a very dark background—this is how you get it.

Astronomik 6nm OIII Transmissions

The FWHM of 6nm is optimized for typical DSLR cameras with CMOS sensors and CCD cameras with a normal/high dark current. With these cameras, the background signal in images taken from heavily light polluted sites is dominated by the dark current of the sensor. In this case, a further reduction of FWHM does not improve the image, as the background will not get darker. Compared 6nm filters this will yield more stars in the field of view which gives you more guiding stars when working with an integrated/dual guiding chip!

Thanks to the MFR coating technique, you may also use one single filter on all instruments up to f/4 without a significant reduction in performance.


Technical data of the filter:

  • Guaranteed transmission of more than 90% at the OIII Line (501 nm)
  • Typical Transmission of 95% at the OIII Line (501 nm)
  • Full-Width-Half-Maximum (FWHM): 6nm
  • Perfect blocking of unwanted light from UV up to the IR
  • Parfocal with all Astronomik filters
  • MFR Coating technique makes it usable with all optics up to f/4
  • Thickness of 1mm
  • Resistant to moisture, scratching, and aging
  • An optically polished substrate, Striae-free, and free of residual stresses
  • High-quality storage box


Filter TypeOIII
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