Narrowband nebula filters, commonly called ultra high contrast (UHC) filters, pass the hydrogen-alpha, hydrogen-beta, and oxygen-III spectral wavelengths and block the rest of the visible spectrum; O-III filters pass only the oxygen-III wavelength. (Since stars are broadband emitters these filters will not help in viewing stars, star clusters, or galaxies – indeed, they will just make those objects more dim.)
A third type of filter called an H-beta blocks all light but the hydrogen-beta wavelength and is only useful for a few specific nebulae, such as the Horsehead Nebula, California Nebula, and Cocoon Nebula, that strongly emit in this line. Finally, there is the LPR (light pollution reduction) filter – a broadband filter intended to mitigate the effect of common light pollution sources such as street lights.
Related category• SPECTRA AND SPECTROSCOPY
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