What does a moon filter do for a telescope?

A moon filter threads into your eyepiece and reduces the brightness of the Moon so you can observe comfortably without eye strain. It cuts glare, enhances contrast on surface features like craters and maria, and prevents the temporary night vision loss that comes from viewing a bright full Moon through a large telescope.

Do I need a moon filter for my telescope?

If your telescope has an aperture of 80mm or larger, yes, a moon filter is strongly recommended. At 100mm and above the Moon becomes blindingly bright without filtration. For very small scopes under 70mm a filter is optional but still improves viewing comfort and surface detail contrast.

What is the best transmission percentage for a moon filter?

For telescopes between 80mm and 150mm a 13% to 25% ND filter works well for most lunar phases. For large telescopes of 150mm and above a 13% filter is better for full Moon viewing. A variable polarizing filter lets you adjust transmission from 1% to 40% or higher so you can match brightness to any lunar phase with a single filter.

Can I use a moon filter to look at the Sun?

No, never use a moon filter for solar observation. Moon filters are not designed to block the dangerous levels of infrared and ultraviolet light produced by the Sun. Looking at the Sun through a moon filter will cause permanent eye damage. Only use a certified full-aperture solar filter designed specifically for solar observation.

What size moon filter do I need for my telescope?

Check the barrel diameter of your eyepieces. If they measure 1.25 inches you need a 1.25 inch filter with M28.5x0.6 threads. If they measure 2 inches you need a 2 inch filter with M48x0.75 threads. Most beginner and intermediate telescope kits use 1.25 inch eyepieces while premium wide-field setups often use 2 inch eyepieces.

8 Best Moon Filters (August 2026) Expert Reviews

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