ZWO Narrowband Filter Set 1.25 inch

Narrowband filters do not eliminate the effects of light pollution or increase the object’s brightness, but rather increase the contrast between nebula and night sky. 

They can reduce the transmission of certain wavelengths of light, specifically those produced by artificial light including mercury vapor, and both high and low pressure sodium vapor lights and the unwanted natural light caused by neutral oxygen emission in our atmosphere (i.e. skyglow).

Technical Parameters:

Name: ZWO New narrowband 1.25″ filter set

Size: 1.25″

Thickness: 5.5mm+3.5mm (thread)

Thread: M28.5*0.6 male thread 

H-Alpha Filter

The ZWO H-Alpha filter has a bandpass of 7nm and passes light at 656nm wavelength, light transmission rate comes up to 80%. 

Technical Data

• FWHM：7±0.5nm
• Glass Thickness 2.0+/-0.03 mm  (1.25”/31mm/36mm)
• Fine-optically polished to ensure accurate 1/4 wavefront  over the both surfaces
• About 90% transmission at H-alpha line 656nm (H-Alpha filter )
• Infrared wavelength 700-1100nm cut-off
• <0.1% transmission of off-band, OD3(Optical Density)

Sulphur II Filter

The ZWO narrowband S-II 7nm filter passes light at a 672nm wavelength with a bandpass of 7nm, which is designed for nebula observation. It is suitable for visual observation on most emission nebulae, planetary nebulae and supernova remnants. Use it with H-alpha and OIII narrowband filters for tricolor CCD astrophotography.

 Technical Data

• FWHM：7±0.5nm
• Glass Thickness 2.0+/-0.03 mm  (1.25”/31mm/36mm)
• Fine-optically polished to ensure accurate 1/4 wavefront  over the both surfaces
• About 90% transmission at SII line 672nm (SII filter )
• Infrared wavelength 700-1100nm cut-off
• <0.1% transmission of off-band, OD3(Optical Density)

Oxygen III Filter

The ZWO narrowband O-III 7nm filter is designed for nebula observation allowing 7nm bandwidth of light centered on a wavelength of 500nm through, which corresponds to OIII emission lines, blocking out all other light. 

Technical Data

• FWHM：7±0.5nm
• Glass Thickness 2.0+/-0.03 mm  (1.25”/31mm/36mm)
• Fine-optically polished to ensure accurate 1/4 wavefront  over the both surfaces
• About 90% transmission at major OIII line 500nm (OIII filter )
• Infrared wavelength 700-1100nm cut-off
• <0.1% transmission of off-band, OD3 (Optical Density)

After putting the filters into the EFW, ensure that the correct side of narrowband filters are facing the telescope and camera.

Transmission Curve