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Optolong OIII 25nm Filter - 1.25" Mounted - OIII-125

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Optolong OIII 25nm Filter - 1.25”

This Optolong OIII filter has a FWHM of 25nm, making it suitable for visual observations of most emission nebulae, planetary nebulae, and supernova remnants with a telescope of at least 6-8”. The OIII broadband filter increases the contrast between the background sky and these objects, so it will also help with observations of bright nebulae, such as the Great Orion Nebula, M42, from light polluted skies. Fainter objects require nights of good seeing and reasonably dark skies for best filter performance. This filter just might allow you to see objects that you’d otherwise miss!

The Optolong Oxygen III Broadband Filter transmits a 25nm bandwidth of light that is centered at 500nm and precision blocks other transmissions, including wavelengths of light that are responsible for light pollution (both artificial and natural).

The Optolong 1.25” OIII 25nm Filter is made with Schott glass that has been multi-coated with an ion-assisted deposition technology to ensure scratch resistance and stability on the central wavelength, or CWL. The filter cell is made of lightweight, strong metal and is CNC machined, sand-blasted, black anodized, and then laser engraved. The result is a super thin filter cell that will produce a clear aperture of 26mm.

Quality Filter Materials:

  • Schott B260 substrate material from Germany, 2.0mm thick
  • CNC machined and black anodized aero-metal filter cell that is ultra-thin to provide largest clear aperture; Laser-engraved to prevent fading
  • Multiple layers of anti-reflection non-cementing coatings applied via electron-beam gun evaporation with Ion-assisted deposition

Optolong Filter Manufacturing Processes and Parameters

  • Filter substrate is fine-optically polished to 1/4 wave and <30 parallelism over both surfaces
  • Surface quality, according to MIL-O-13830, is 60/40
  • 90% transmission at 495.9nm and 500.7nm
  • 0.1% transmission Hg at 435nm and 578nm
  • 0.1% transmission Na at 589nm
  • High value transmission of pass-band and optical density of off-band is assured through Optolong’s planetary rotation system, a homogenous and precise coating procedure
  • Thin metal cells have a clear aperture of 26mm for 1.25” filters
  • Each filter comes with a plastic case with high pressure EVA case lining

About Optolong

Optolong is the Astronomy Filters division of Yulong Optics, an optical filter design and processing company out of Kunming, China that has provided filters for over 700 optical companies since 1999. All Optolong filters pass European Union RoHS requirements and have been certified by TUV Rheinland and Bureau Veritas.