ZWO Filter Set H-alpha SII OIII 31mm unmounted

ZWO Filter Set H-alpha SII OIII 31mm unmounted

This 31 mm unmounted ZWO narrowband set contains separate H-alpha, SII and OIII filters for emission-nebula imaging. Each channel isolates a selected emission band so that calibrated exposures can be combined into SHO or other narrowband palettes.

Passbands and rejection

The manufacturer technical data specifies a 7 ± 0.5 nm FWHM, approximately 90% transmission at the respective H-alpha 656 nm, SII 672 nm and OIII 500 nm lines, off-band transmission below 0.1% (OD3), and infrared blocking from 700 to 1100 nm. Filtering increases contrast against unwanted wavelengths; it does not increase the object’s emitted brightness.

Glass and mounting

The 31 mm unmounted version uses 2 mm glass with ±0.03 mm thickness tolerance. Use a holder designed for the stated unmounted diameter. ZWO specifies 1/4-wave optical polish over both surfaces.

Capture workflow

Use the three filters separately, normally with a monochrome camera and compatible filter wheel. H-alpha data can also be blended with broadband RGB exposures to add emission structure. Match the filter size to the holder and optical cone to avoid mechanical obstruction.

ZWO manufacturer documentation

Compatibility notes

Use the exact named-model manufacturer connection and operating instructions linked with this product. Optional parts and adapters require their specified spacing and power limits.

Additional specifications