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

No. The AAS says filters that thread into an eyepiece at the back of the telescope are dangerous for solar viewing. A solar filter must be attached securely to the front of the telescope.

Fixed or variable Moon filter?

A variable filter lets you adjust transmission, 1 to 40% on Celestron's, per the listing. A set of fixed ND filters (13%, 25% and 50% in Celestron's set) does a similar job by swapping or stacking.

Moon Filters for Telescopes: Fixed, Variable and ND Sets

Q: What does a Moon filter do?

It dims the Moon's glare so you can see more surface detail. Celestron's listing says its Moon filter reduces glare and increases contrast, and is also useful on very bright planets.

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Quick answerThrough any decent telescope, a bright Moon is dazzling. A Moon filter threads onto your eyepiece and dims it so the craters stand out. Celestron makes a simple fixed filter, a variable one you twist from 1 to 40% transmission, and a set of 13%, 25% and 50% ND filters, per the listings. Important: a Moon filter is not a solar filter. Never use one on the Sun.

Your first look at a gibbous Moon through a telescope can be almost too bright. A Moon filter is a small, cheap fix. Product details are from the listings; we haven't tested them.

Not for the Sun. The American Astronomical Society says solar filters "designed to thread into an eyepiece at the back end of the telescope ... are dangerous." A Moon filter threads into the eyepiece and blocks far too little light. For the Sun, use a front-mounted filter made for solar viewing: see solar filters.

Your options

Fixed Moon filter

Celestron's 1.25 inch Moon filter reduces glare and increases lunar contrast, and the listing says it's also useful on extra-bright planets and for daytime viewing over sand or snow.

Simple, threads on

Celestron Moon Filter (1.25 in.)

Cuts glare and boosts lunar contrast, per the listing
Threads onto most 1.25 in. eyepieces
Not a solar filter

Check price on Amazon

Variable Moon filter

Rotate the lower ring to set light transmission anywhere from 1 to 40%, per the listing. Useful because the Moon's brightness changes a lot between crescent and full.

Adjustable 1-40%

Celestron Variable Moon Filter

Adjustable 1-40% light transmission, per the listing
Rotate the lower ring to dim
Threads onto Celestron 1.25 in. eyepieces
Not a solar filter

Check price on Amazon

Moon filter set

Three neutral density filters (13%, 25% and 50%) plus a Moon & Sky Glow filter, in stackable aluminum cells with a Moon map, per the listing.

3 ND + sky glow + Moon map

Celestron Moon Filter Set

Three ND filters: 13%, 25% and 50% transmission, per the listing
Moon & Sky Glow filter
Stackable aluminum cells; case with Moon map
Not a solar filter

Check price on Amazon

Other ways to get one

Celestron's 1.25 inch accessory kit and the SVBONY SV233 kit both include a Moon filter alongside eyepieces. The NexGo DX kit pairs a 13% Moon filter with a phone adapter for snapping lunar photos, per the listing.

Kit with Moon filter

Celestron Eyepiece, Barlow & Filter Kit (1.25 in.)

5 Plossl eyepieces: 32, 17, 13, 8 and 6 mm, per the listing
2x Barlow lens
Moon filter plus colored planetary filters
Foam-lined hard case

Check price on Amazon

Phone adapter + Moon filter

Celestron NexGo DX Kit (Phone Adapter + Moon Filter)

Phone adapter for eyepieces 25.4-44.45 mm across, per the listing
Bluetooth shutter remote
13% transmission Moon filter

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Tips

The Moon is often most dramatic near first or last quarter, when shadows along the terminator show crater depth.

More targets in what you can see with a telescope.

FAQ

What does a Moon filter do?

Cuts glare and boosts contrast.

Can I use it on the Sun?

No, never.

Fixed or variable?

Variable adjusts; a set swaps or stacks.

Moon Filters: Taming the Glare (and Why They're Not Solar Filters)