The OIII-CCD 7nm Photographic Filter is designed for nebula observation. Allowing 7nm bandwidth of light centered on a wavelength of 500nm through. Which corresponds to OIII emission lines and adds in reducing 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. Also including the unwanted natural light caused by neutral oxygen emission in our atmosphere (i.e. skyglow).