Filters for telescopes
There are three main types of filters for telescopes:
Also called light-pollition or LP filters, these work by blocking all wavelengths of light except those transmitted by the ionized atoms of hydrogen, oxygen and sulfur found within nebulae and supernovae remnants. These filters can be narrowed down to broadband, narrowband, O-III, H-beta, and S-II.
Planetary filters are colored filters used to accentuate or increase contrast for features on planets, such as the bands of Jupiter, ice caps on Mars, or features on the moon. They often come in a set.
Solar filters are used to safely view the sun through a telescope and come in three major groups: full aperture, off-axis (reduced) aperture, and threaded. Solar filter are also available for binoculars.