Narrowband filters aren't a fix-all for light pollution or for making celestial objects appear brighter. What they can do, however, is improve the contrast between a nebula and the surrounding night sky without actually making the nebula brighter.

These filters are effective at blocking certain light wavelengths, notably those originating from artificial sources like mercury vapor lights, as well as high and low-pressure sodium vapor lights. They also mitigate the unwanted natural light due to neutral oxygen emissions in Earth's atmosphere, commonly known as skyglow.

Since 2018, ZWO has upgraded its narrowband filters, offering improved performance in line with new standards.

Technical Specs:

Product Name: ZWO 31mm narrowband filter
Diameter: 31mm
Thickness: 2mm

The ZWO H-Alpha filter features a 7nm bandpass and allows light at a 656nm wavelength to pass through, achieving a light transmission rate of up to 80%. This makes it an ideal choice for high-contrast H-alpha astrophotography, allowing you to capture intricate nebula details, even in areas with significant light pollution. Get ready for an endlessly enjoyable astrophotography experience!

Specifications

FWHM：7±0.5nm
Glass Thickness 2.0+/-0.03 mm (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 )
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
<0.1% transmission of off-band, OD3(Optical Density)

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ZWO 31mm Ha filter 7nm

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