This 36mm round ZWO Narrowband HA, SII & OIII Filter Set can help you observe and photograph spectacular emission nebulae. The filters pass hydrogen-alpha light at 656nm, sodium II at 672nm, and oxygen III at 500nm, resulting in photos with high contrast. They also reduce artificial light from streetlights and natural but unwanted light caused by neutral oxygen emission in the earth's atmosphere. Each filter is 2mm ± 0.03nm thick.
- FWHM：7 ± 0.5nm
- Glass Thickness 2.0 ±: 0.03 mm
- Fine-optically polished to ensure accurate 1/4 wavefront over the both surfaces
- About 90% transmission at H-alpha line 656nm (H-Alpha filter)
- About 90% transmission at SII line 672nm (SII filter)
- About 90% transmission at major OIII line 500nm (OIII filter)
- Infrared wavelength 700-1100nm cut-off