Telescope Filters | How to Use a Telescope | Part 5

Astronomical eyepiece filters are a wonderful way to enhance your telescope viewing experience.

Telescope filters work by blocking specific parts of the light spectrum, while allowing other wavelengths of light to pass through.

Filters can also help reduce light scatter and light pollution, improve contrast, and reveal subtle detail in celestial objects that would otherwise be invisible.

Eyepiece filters are available in one and a quarter and two-inch sizes and are compatible with most telescope eyepieces.

How to Use Telescope Filters

To use one simply screw it onto the bottom of the eyepiece barrel and insert the eyepiece into a telescope diagonal or focuser.

Coloured filters are an exceedingly popular observing tool and come in a wide range of colours.

They help increase contrast and bring out details on a planet surface or in its cloud structure. For example, a red filter enhances Mars polar ice caps and surface features, while a green filter is useful for observing Jupiter’s cloud belts and increases visibility of its famous Great Red Spot.

Telescope Filters | How to Use a Telescope | Part 5

Experimenting with Telescope Filters

It is fun to experiment using different coloured filters to see what each filter will reveal.

You can also try stacking coloured filters to enjoy the benefits of multiple filters at the same time, we recommend using a telescope with a large aperture if stacking filters to keep your views bright.

A Moon filter is essential for observing our closest celestial neighbour.

The reason for this, is that it reduces the brightness of the Moon’s glare and improves surface details such as craters, mountain ranges, seas, and valleys.

These will become more easily visible with increased contrast during all lighted phases.

Telescope Filters | How to Use a Telescope | Part 5

Neutral Density Filters

Like the moon filter, a neutral density filter darkens the moon’s bright glare. This filter also brings out faint detail and other bright objects without changing their natural colour like a colour filter would.

Neutral density filters come in handy for splitting closed double Stars when one Star is significantly brighter than the other.

Telescope Filters | How to Use a Telescope | Part 5

Other Telescope Filters

Ultra-high contrast light pollution reduction filters are designed to selectively reduce the transmission of artificial lighting such as light emitted by streetlamps and natural sky glow.

An LPR filter will darken the sky background and is the perfect filter for viewing deep sky objects in light polluted urban skies or boosting the contrast of Nebulae in Dark Sky sites.

Telescope Filters | How to Use a Telescope | Part 5
An Oxygen filter is a narrowband filter which isolates the two doubly ionised oxygen lines emitted by planetary and emission nebulae, while blocking the rest of the overall spectrum of light. The result is extreme contrast between the black sky background and faint O3 light.

Views of deep sky objects such as the Veil, Ring, Dumbbell, Crescent and Orion Nebulae benefit greatly from an O3 filter.

Visual filters should be an essential part of everyone’s observing kit. Thanks for reading and wishing you all clear skies.

 How to Use a Telescope | Part 5 | Telescope Filters

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