Oxygen III - This is the highest contrast Nebula Filter in the series, a line filter for only the two emission lines of oxygen. A great choice for observations of supernova remnants and other nebulae that glow in OIII. Other types of objects that glow in all parts of the visible spectrum (e.g. galaxies) are reduced visibly, but some normally invisible regions of nebulae are clearly visible. This filter fits all standard 2.0-inch eyepieces and filter wheels.