Oxygen III (OIII) narrowband filters are made so only a small portion of light pass through the filter, resulting in diffuse and planetary nebulae to appear more clearly against a blacker background of space. There are two kinds of OIII filters: visual filters and astrophotography (CCD) filters.
Visual OIII filters will enhance the contrast of nebulae, revealing more detail than what can be seen when viewed without an OIII filter. Visual OIII filters are best used when paired with telescopes 6" (150mm) or larger. Astrophotography OIII filters are suitable for imaging nebulae from dark skies and from light polluted areas.