Using an LP filter blocks out some of the optically saturating mercury and sodium emission lines, and allows enough contrast to make seeing a bit more productive in light-pollution areas. Lumicon, Meade, Orion, Thousand Oaks, and many other optical manufacturers have developed specialty filters in this category. Narrowband filters are primarily designed for viewing many emission nebula. These filters may allow only the bright pair of emission lines of Oxygen III, the Hydrogen Beta emission line, and the wavelengths between H-beta and the OIII to get through. Without special narrowband filtering, many of the fainter nebula could not been seen.
Contrast is improved because of darkening of the background skyglow.
UHC and the Meade Ultrablock can, at times, show the Rosette Nebula to the unaided eye when you look through them. The stars in the field will dim somewhat, but the planetary nebula will remain standing out from the background stars. The following is a table of common filters, and some notes concerning each, however, remember that the characteristics in the notes are not exclusive. When reading the notes and characteristics of some of these filters, many of them have a lot in common. Enhances images of comet dust trails and heads.