Best Solar Filters for Telescopes: Three Options and How to Use Them Safely

A solar filter is the cheapest accessory that opens up the biggest part of the sky. With one, your daytime telescope shows sunspots, and your telescope earns its keep during the hours when nothing else is up. It is also the accessory that matters most for safety, since a bad filter, or no filter, can cause permanent eye damage.

This guide covers three common options: a ready-made telescope filter, filter film that you mount yourself and eclipse glasses for naked-eye viewing. It also lists the checks to do before you use any of them. Please read our safe solar viewing guide first, since it covers the rules that apply to all of them.

The rule that matters most

Solar filters for a telescope go over the front of the telescope, covering the full opening, so that sunlight is reduced before it enters the tube. Never use a filter at the eyepiece, and never use any gear that is not made for solar viewing. If a filter is scratched, torn or has pinholes, do not use it.

The three options

Celestron EclipSmart Universal Solar Filter: ready-made telescope filter

The EclipSmart Universal Solar Filter is a ready-made filter that fits over the front of a telescope. It is a simpler option than building your own, since there is nothing to cut or mount. It has a large number of buyer ratings and a low price.

The key question is fit. A filter has to sit snugly so that wind cannot knock it off, and it has to cover the whole opening of your telescope. Check the listing for sizes and compare them with your scope's tube diameter. Inspect it before each use.

Buy it if you want a ready-to-use telescope filter. Skip it if your telescope is outside the listed sizes.

Solar Filter Sheet 8 x 8 inch: low-cost filter film

Filter film is the traditional low-cost route. You cut a piece of the film, mount it in a cell that fits the front of your telescope and secure it so it cannot come loose. A single sheet can make several filters, and it works on telescopes of many sizes. The listing has a high buyer rating.

The catch is that you have to build the cell yourself, and the film needs careful handling. A crease or a pinhole can let harmful light through. Make sure the listing says the film is safe for visual use, since some are made for photography only.

Buy it if you are comfortable building a filter cell. Skip it if you want something ready to use.

Celestron EclipSmart Solar Shades Observing Kit: eclipse glasses, naked eye only

Solar glasses let you look at the Sun with the naked eye, and they are a good way to check for sunspots or watch an eclipse. This kit has several pairs and a guidebook, and a large number of buyers have rated it highly.

They are for naked-eye viewing only. Never put them in front of a telescope, binoculars or a camera, and never wear them under a telescope eyepiece. They also need to be in good shape, so throw them away if they are scratched.

Buy it if you want to view the Sun or an eclipse with the naked eye. Skip it if you plan to use a telescope, since you need a front filter.

Side-by-side specs

Checks to do before every solar session

1. Look at the filter against a bright light. You should see no pinholes, scratches, tears or wrinkles.
2. Test the fit. Wiggle it. A loose filter can blow off.
3. Cover the finder. Put a cap on it or remove it, since it will focus sunlight too.
4. Aim by the shadow. Do not look along the tube.
5. Never leave the scope unattended. Kids and pets can cause problems in seconds.
6. Know your exit plan. If the filter comes off, move away from the eyepiece and cap the scope.

What you can see with a filter

A white-light filter shows sunspots, and sometimes finer granulation. Sunspots shift from day to day as the Sun rotates, and you can follow groups for a week or two. Our guide on what you can see through a telescope covers more. Solar prominences and fine surface detail need a special hydrogen-alpha telescope, which is a different class of equipment.

Common mistakes

Using a filter that is too loose. A gust of wind can remove it.

Using eclipse glasses with a telescope. Not safe.

Skipping the finder cover. The finder can focus enough light to burn.

Forgetting to check for damage. Film wears out, and the filter you used last year may have a pinhole now.

Buying the wrong grade of film. Photography-grade film may not be safe for the eye.

Storing your filter

Keep a filter in its case or a clean envelope, away from sharp objects and extreme heat. Do not stack heavy items on it. Check it before every use, and replace it if there is any doubt.

If you have kids

Children can enjoy solar viewing with supervision. Make the rules clear, and keep the filter out of reach when you are not using it. For scopes that suit children, see telescopes for kids.

How to build a film filter cell

If you buy filter film, the cell is the part that keeps you safe. A simple cell is two rings of stiff cardboard or plastic, cut so that the film sits between them without wrinkles, with a collar that fits over the front of your telescope and a snug friction fit. Use tape or glue only on the cell, and keep it away from the film's center. The film should be flat but not stretched, and no part of the opening should be unfiltered.

Wrap the cell so that it cannot slip. Many people add a strap, a piece of foam or a few layers of tape around the telescope tube to give the cell a firm seat. After you mount the film, hold it up to the Sun with your eyes closed, then open them only to check the glow through the film from a short distance. Look for any bright pinpoints, which indicate a hole. If you see even one, replace the film.

Because the build quality is up to you, many beginners prefer a ready-made filter. That is a sensible choice, and the main reason the ready-made filter has a place here.

Choosing between white-light and other filters

The filters on this page are white-light filters, which show the Sun's visible surface: sunspots and sometimes granulation. Other types exist, such as hydrogen-alpha telescopes, which show prominences and surface detail in red light. They are specialized, they cost far more and they are a separate hobby. For a first solar setup, a white-light filter is the right choice.

White-light filters come in different colors. Some make the Sun look orange, and others make it look white or blue-white. The color is a matter of taste, and it does not change how safe the filter is. What matters is that the filter is rated for visual solar viewing and fits your telescope.

What a filter does and does not protect

A front filter protects your eye and the telescope's optics from the intense light and heat. It does not protect you from other mistakes. If the filter falls off, you can still be injured. If you point a finder at the Sun, the finder is unprotected. If you use an eyepiece filter instead of a front filter, the heat can crack it. This is why the habits in our safe solar viewing guide matter as much as the filter itself.

Using a filter with different telescope types

Reflectors, refractors and compound scopes all use front filters. For a Dobsonian with an open tube, the filter fits over the front opening and has to be held firmly. For a refractor, the filter fits over the dew shield or the lens cell. For a compound scope like the NexStar, it fits over the front corrector plate. Check that your filter fits the front of your tube, and measure the outer diameter of the tube before you buy. If you are comparing scopes, see our beginner telescope list.

How we chose these options

We compared the listing information, the intended use and the buyer ratings of common solar viewing products on Amazon. We cannot verify safety ratings ourselves, so we point you to the maker's information and to the rules above. This is research, not hands-on testing. Prices come from Amazon and are stamped with the time they were checked. See our about page and affiliate disclosure.

Which one should you buy?

For a telescope, buy a filter made to fit the front of it, such as the EclipSmart Universal Solar Filter if it fits your scope, or use filter film if you are comfortable building a cell. Buy eclipse glasses for naked-eye viewing, and never mix them up with telescope gear. For a general guide to scopes, see our beginner telescope list.