Narrowband filter does not eliminate the effects of light pollution or increase the object’s brightness. In many cases, they increase the contrast between nebula and night sky, not brightening the nebula. It 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). Form 2018, ZWO Made a progress on narrowband filters with the new standard, provide better performance. 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 ) 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) Transmission Curve
