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Optolong H-Beta 25nm Filter - 2" Mounted - HBTA25-200

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Optolong H-Beta 25nm Filter - 2”

This Optolong H-Beta filter has a FWHM of 25nm, making it more suitable for visual observations of the Horsehead, California, and Cocoon nebulae. The filter transmits a 25nm bandwidth of light that is centered at 486nm and precision blocks other transmissions, including wavelengths of light that are responsible for light pollution (both artificial and natural). When you use the 25nm H-Beta filter, you’ll notice that the contrast between the background sky and objects that emit H-Beta light increases. This allows you to see these elusive objects more easily, but you will still need a telescope with an aperture of at least 8” and a night of good seeing.

The Optolong 2” H-Beta 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 45mm.

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 H-Beta 486nm
  • 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 45mm for 2” 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.