Used ZWO O-III 2" 7nm Filter


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  • $174.95
  • Regular price $249.99

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This is a ZWO O-III 2" filter in excellent condition.  The optics and body are clean.  This filter was part of a set of three (H-Alpha, S-II, and O-III) that we are selling separately.  It comes in its original jewel case and box.  




ZWO 2" H-Alpha, SII, OIII 7nm Filter Set

Narrowband filters are a fantastic astrophotography tool when it comes to imaging during times of high light pollution. When all three filters, the H-alpha, SII, OIII filters, are used in unison, it is perfect for tricolor CCD astrophotography!

While narrowband filters do not eliminate the effects of light pollution, they do enhance the contrast between celestial objects and the night sky. It provides this contrast by reducing the transmission of certain wavelengths of light. These wavelengths come from artificial light, mercury vapor and both high and low pressure sodium vapor lights, and natural light, such as skyglow caused by neutral oxygen emission in the atmosphere. Additionally, each filter is fine-optically polished to ensure an accurate 1/4 wavefront.

ZWO Narrowband 2" Filter Set Specifications


  • Filter Size: 2″
  • Mechanical Thickness: 7.5mm (5mm + 2.5mm thread)
  • Thread: M48.5x0.75 male thread
  • FWHM: 7±0.5nm
  • H-Alpha Transmission Rate: About 90% transmission
  • SII Transmission Rate: About 90% transmission
  • OIII Transmission Rate at 500nm: About 90% transmission
  • Infrared wavelength cut-off: 700-1100nm
  • Transmission of off-band: <0.1%, OD3(Optical Density)


ZWO H-alpha 7nm Filter

ZWO H-alpha 7nm filter is a 2" filter with a M48x0.75 male thread. The bandpass of the filter is 7nm, and it passes light at 656nm wavelength. If you want high contrast astroimaging, then this Hα filter will deliver an excellent performance. The light transmission rate for the filter comes up to 80% and the glass has been fine-optically polished to ensure accurate 1/4 wavefront. So, even in areas of strong light pollution, you can still explore the night sky with your imaging equipment!

ZWO SII 7nm Filter

ZWO's SII 7nm filters passes light at a 672nm wavelength and is fine-optically polished to ensure accurate 1/4 wavelength. With this wavelength transmission, the SII filter is most suitable for nebula observation and imaging. When it comes to visual observation, it works best with most emission nebulae, planetary nebulae, and supernova remnants.

ZWO OIII 7nm Filter

The OIII 7nm 2" filter from ZWO is a designed specifically for nebula observation. By allowing 7nm bandwidth of light through a wavelength of 500nm, the OIII will block out all other light other than that which corresponds with the OIII emission lines. Using this filter goes beyond RGB filter use, as it will allow you to capture the beauty of many different nebulas, even in light polluted skies!