Telescope Eyepiece Filters

An eyepiece filter can bring out detail in an object, assist with astrophotography, and help reduce the effects of light pollution. The type of filter to use depends on what you are observing.

Types of Filters for Astronomical Viewing

Moon Filter

The moon is a beautiful sight even in a small telescope, however the moon is very bright and using a moon filter can save your night vision. Moon filters are usually neutral density (gray) or variable polarizing filters. Cutting the glare makes mountains and craters more comfortable to study, and it reduces irradiation, which is the distortion at the boundary between light and dark areas, such as along the lunar terminator. more...

Broadband Light Pollution Filter

A broadband light pollution filter is designed to block the wavelengths given off by mercury-vapor and sodium-vapor lights. In doing so it also dims stars, star clusters and galaxies slightly. The main light of emission nebulae falls at other wavelengths and passes through, so these filters help most on nebulae, but of the nebula filters this is the least effective. They do little against white LED lighting, which shines across the whole spectrum. more...

CLS (City Light Suppression)

CLS telescope eyepiece filters are designed to reduce the effects of light pollution, making them ideal for urban or suburban stargazing. These broadband filters work by blocking common artificial light wavelengths, such as mercury and sodium vapor emissions, while passing the main emission lines of nebulae and much of the light of stars and galaxies. This improves contrast on emission nebulae under skies lit by those older lamps; the gain on galaxies and star clusters is small, and white LED lighting cannot be filtered out. CLS filters also dim stars slightly and are not recommended for planetary observation. more...

UHC

UHC (Ultra High Contrast) telescope eyepiece filters are specialized astronomical accessories designed to enhance the visibility of deep-sky objects such as nebulae. They work by passing a narrow band around the key emission lines from nebulae (Oxygen-III at about 496 and 501 nm and Hydrogen-beta at 486 nm) while blocking most other light, including artificial and natural skyglow. This results in higher contrast and better detail, making them ideal for viewing emission and planetary nebulae under both light-polluted and dark-sky conditions. However, UHC filters do not help galaxies, star clusters or reflection nebulae, whose light is spread across the whole spectrum. more...

Oxygen III

Oxygen III (OIII) telescope eyepiece filters are specialized filters used by amateur astronomers to enhance the visibility of certain deep-sky objects, particularly planetary nebulae and supernova remnants. They work by isolating the specific wavelengths emitted by doubly ionized oxygen (around 496 and 501 nm), which are prominent in these objects. By blocking other wavelengths, OIII filters increase contrast and detail, making faint structures more pronounced against the background sky. They are especially effective in light-polluted areas or under bright moonlight, helping to bring out nebular features that would otherwise be difficult to observe. more...

Hydrogen-Beta

The H-beta eyepiece filter passes a narrow band around the hydrogen-beta line at 486 nm. It helps only a short list of objects, such as the California Nebula and IC 434, the glowing background that makes the Horsehead Nebula easier to see. It can also help a few other faint hydrogen nebulae.

This is our list of telescope eyepiece filters. Eyepiece filters can bring out detail in an object, assist with astrophotography, and help reduce the effects of light pollution. The type of filter to use depends on what you are observing. more...