# Nebula filter

Also called: UHC, OIII, O-III, H-beta, Hβ, narrowband filter, LPR filter, light pollution filter.

A filter that passes the light emitted by nebulae and blocks most skyglow, making them stand out.

[Emission nebulae](https://astropilot.space/glossary/emission-nebula), [planetaries](https://astropilot.space/glossary/planetary-nebula) and [supernova remnants](https://astropilot.space/glossary/supernova-remnant) shine in a few narrow colours. A UHC (narrowband) filter passes hydrogen-beta and oxygen-III light; an OIII filter passes only oxygen — superb on planetaries and the Veil; an H-beta filter is the key to a few objects like the Horsehead and California Nebula.

Galaxies, star clusters and reflection nebulae shine with ordinary starlight: nebula filters only dim them.

**At the eyepiece:** Filters work best with a fairly large [exit pupil](https://astropilot.space/glossary/exit-pupil) (3–6 mm).

**In AstroPilot:** Object pages say which filter suits each object, and whether you own one.

**Examples:** [NGC6960](https://astropilot.space/object/NGC6960.md), [M27](https://astropilot.space/object/M27.md), [B33](https://astropilot.space/object/B33.md), [M42](https://astropilot.space/object/M42.md)

**Related:** [Emission nebula](https://astropilot.space/glossary/emission-nebula.md), [Planetary nebula](https://astropilot.space/glossary/planetary-nebula.md), [Contrast](https://astropilot.space/glossary/contrast.md), [Light pollution](https://astropilot.space/glossary/light-pollution.md)

From the AstroPilot astronomy glossary: https://astropilot.space/glossary/nebula-filter