The best solar filter for a telescope is a certified white-light filter that clamps or straps over the front aperture of the tube before any sunlight enters the optics. Aluminized polyester film in a rigid cell, meeting ISO 12312-2, is the standard most of our picks use. Never fit a filter at the eyepiece end, and never use eclipse glasses on a telescope.
Read this before anything else. Concentrated sunlight can burn your retina permanently in a fraction of a second through a telescope, spotting scope or binoculars, and it can also damage the diagonal, the eyepiece and any glass optics in the path. A solar filter must sit over the front aperture, above the main lens or mirror. Eyepiece-mounted solar filters are the single most dangerous mistake beginners make, because forum moderators have long warned they should never be used for solar viewing at any magnification, and eclipse glasses do not survive the concentration a telescope creates.
Sunspots are the reason most people buy a solar filter in the first place. A white-light filter strips the Sun down to a comfortable white or orange disc with dark spots scattered across it, and on a steady day you can follow those spots as they grow, rotate across the disc and fade over a couple of weeks.
There is a second layer to this hobby. H-alpha observing reveals prominences, filaments and the mottled chromosphere in deep red, and that requires a completely different architecture. As one Cloudy Nights poster put it plainly, H-alpha solar astronomy uses etalons, not plain filters that you screw in the eyepiece, and the safest bet for H-alpha is a dedicated solar telescope. We stay with white light here, because that is what the eight filters below all do.
This roundup covers eight genuine white-light solar filters built for telescope sun viewing, from cut-to-size film sheets you mount yourself to factory ISO 12312-2 cells with hook-and-loop straps. We worked from the published specifications, the certification claims, the fit ranges and the review histories, and we tell you plainly where each one is strong and where it frustrates people.
Before you pick, it is worth reading our telescope eyepiece guide, because the eyepiece you choose for solar work matters almost as much as the filter and the magnification changes what you can resolve.
Table of Contents
- Top 3 Solar Filter Picks in 2026
- Every Solar Filter in This Roundup Compared
- 1. Thousand Oaks 6×6 Solar Filter Sheet: the Most Reviewed Filter in the Roundup
- 2. Thousand Oaks 8×8 Solar Filter Sheet: The Budget Pick for Big Apertures
- 3. Celestron EclipSmart 8 Inch Solar Filter: Premium Pick for Celestron SCT Owners
- 4. Celestron EclipSmart Universal Solar Filter: One Filter for Scopes, Spotting Scopes and Cameras
- 5. Thousand Oaks 12×12 Solar Filter Sheet: Best for Large Apertures and Multi-Instrument Kits
- 6. Celestron EclipSmart Filter for 127mm and 130mm Reflectors: Best for Small Reflectors
- 7. Astromania Deluxe Filter 100mm: Best for a Rigid Aluminium Cell
- 8. Rainbow Symphony 70mm Solar Filter: The Best Value for Smaller Tubes
- How to Choose a Solar Filter for Your Telescope
- How to measure your aperture and match the cell size
- Film or glass, and what optical density means
- Why ISO 12312-2 matters and what uncertified stock actually is
- Finding the Sun without a finderscope
- A pre-use pinhole check and how to store the filter
- Solar eclipses and photographing the Sun
- H-alpha filters and solar wedges are a different category
- Jupiter and Moon filters are also a different category
- Frequently Asked Questions
- What filter do you need to look at the sun with a telescope?
- What is the best solar filter for a telescope?
- Is it safe to look at the Sun through a telescope?
- What happens if you look at the Sun through a telescope without a solar filter?
- What type of telescope is best for viewing the Sun?
- What lens filter do I need for a solar eclipse?
- Which Solar Filter to Buy First
Top 3 Solar Filter Picks in 2026
Thousand Oaks 6×6 Solar Filter Sheet
- Cut-to-size black polymer film
- Works with telescopes and cameras
- Most reviewed filter in the roundup
- Lowest-cost way to build a filter
Thousand Oaks 8×8 Solar Filter Sheet
- Substrate-embedded filtering
- Five-year guarantee
- Larger sheet for big front cells
- 4.6 rating across 947 reviews
Celestron EclipSmart 8 inch Filter
- ISO 12312-2:2015(E) compliant
- Fits Celestron 8 inch SCT and EdgeHD
- Hook-and-loop straps
- Two-year warranty
Every Solar Filter in This Roundup Compared
| Product | Specifications | Action |
|---|---|---|
| Thousand Oaks 6×6 Solar Filter Sheet |
|
Check Latest Price |
| Thousand Oaks 8×8 Solar Filter Sheet |
|
Check Latest Price |
| Celestron EclipSmart 8 inch Solar Filter |
|
Check Latest Price |
 Celestron EclipSmart Universal Solar Filter |
|
Check Latest Price |
 Thousand Oaks 12×12 Solar Filter Sheet |
|
Check Latest Price |
 Celestron EclipSmart Filter for 127mm and 130mm Reflectors |
|
Check Latest Price |
 Astromania Deluxe Filter 100mm Metal Cap |
|
Check Latest Price |
 Rainbow Symphony 70mm Black Polymer Filter |
|
Check Latest Price |
1. Thousand Oaks 6×6 Solar Filter Sheet: the Most Reviewed Filter in the Roundup
Thousand Oaks Optical 6″x6″ Solar Filter Sheet for Telescopes, Binoculars and Cameras
6 x 6 inch black polymer sheet
Model BP-6X6
Cut, sized and mounted by you
For telescopes, binoculars and cameras
Pros
- Lowest-cost way to build a filter for any aperture
- Shows sunspots and granulation in a natural orange tone
- Cut-to-size format suits odd front cell sizes
- Top seller in Telescope Filters with 1097 reviews
Cons
- You must cut and secure the sheet yourself
- Bare sheet can crease if handled carelessly
This is the sheet we kept coming back to while comparing all eight. Thousand Oaks has been making safe solar filters for more than 30 years, and this 6×6 inch black polymer sheet is the raw material that a lot of careful observers start with. It shows sunspots and granulation, which are the two things you actually want on a white-light view.
The honest headline is that this is not a finished product. You cut it to size, mount it over the front aperture of your telescope, binocular barrel or camera lens, and you secure it yourself. The manufacturer’s own warning is blunt about this: always make sure the filter is well attached, using sticky tape, to keep it from falling while observing. That instruction exists for a reason, and it is the whole trade-off of this option.
With 1097 reviews at a 4.6 average and 78 percent five-star ratings, the pattern in the reviews is very consistent. Buyers treat it as dependable raw material rather than a turnkey accessory, and the ones who are happy are the ones who mounted it carefully. The material renders the Sun in a natural orange colour, which most people find easier on the eyes than a neutral white disc.
The useful part of the format is that it solves sizing entirely. If your front cell diameter is some awkward number that no off-the-shelf ring covers, a sheet you cut yourself handles it. If you have three instruments, you cut one piece per instrument and use the rest later.
Who this filter suits
Anyone who wants white-light sunspot viewing and already knows how to mount a filter securely. It is also the natural choice for binoculars, since you can cut two identical pieces rather than buying a matched pair of factory cells. Cameras work too, which makes it a natural companion to a white-light solar photography setup.
If you want to compare it against how a premium eyepiece handles planetary and lunar work, our guide to the best telescope eyepieces for planetary viewing is worth a look. You will be using the same optical train in both cases.
Who this filter does not suit
First-time owners who have never fitted a filter. Nothing here holds itself in place, and the safety of the whole setup rests on your own mounting. It is also a poor choice if you want a rigid, protected cell that survives being bumped in a car boot.
And it does not help you see prominences or the chromosphere. No white-light filter does. If that is what you are after, you need a dedicated solar telescope.
2. Thousand Oaks 8×8 Solar Filter Sheet: The Budget Pick for Big Apertures
8″x8″ Solar Filter Sheet for Telescopes, Binoculars and Cameras
8 x 8 inch black polymer sheet
Model BP-8, weighs 1.6 ounces
Filtering embedded in the substrate
Five-year guarantee
Pros
- Filtering properties sit inside the substrate not on it
- Five-year manufacturer guarantee
- One sheet covers large Dobsonian front cells
- 4.6 stars across 947 reviews
Cons
- You still have to cut and secure the sheet
- Unsupported film must be handled without creasing
The 8×8 inch sheet is the same idea as our top pick with more material, and it earns its place for a specific reason. If you own a 10-inch or 12-inch Dobsonian, this is the size that lets you cover the entire front cell with one piece and still have margin around the rim for taping. The 6×6 inch sheet can be tight on those instruments.
The specification worth noting is in the construction. This version describes its filtering properties as protected within the substrate rather than coated on the surface, which is why the maker can call it stronger than Mylar and back it with a five-year guarantee. Surface coatings can scratch and degrade. Substrate-embedded filtering does not have that failure mode.
At 947 reviews and 4.6 stars, with 76 percent five-star ratings, this is one of the most stable review profiles in the roundup. Owners highlight durability of the film and the freedom to size a filter for any instrument. The critical minority, around 2 percent at one star, tend to concentrate on handling rather than performance.
Weight is not a factor at all here. The sheet weighs 1.6 ounces, so it adds nothing to what you carry to a star party or a public solar outreach session.
What to check before you mount it
Measure your front cell’s outside diameter with a caliper or a ruler and add at least half an inch of overlap on every side so the taped edge grips a surface rather than a corner. Cut with a sharp blade in one stroke to avoid a ragged edge, and trim around the rim of the tube so there is no optical surface exposed underneath.
Then hold it up to a lamp or a bright window before you attach it. Look for pinholes. Any light point you can see through the film is a defect and the sheet should not go near an aperture.
Where it is the wrong pick
If you want a filter that snaps on and stays on by itself, this is the wrong format twice over. The absence of a cell means no clamp, no strap and no mechanical retention, and the manufacturer is explicit that attachment is your responsibility.
It is also not the right answer for outreach work where strangers will handle the telescope. In a public setting you want hardware retention, not tape.
3. Celestron EclipSmart 8 Inch Solar Filter: Premium Pick for Celestron SCT Owners
Celestron EclipSmart 8″ Solar Safe Eclipse Telescope Filter – ISO Compliant
ISO 12312-2:2015(E) compliant
Fits Celestron 8 inch SCT and EdgeHD
Weighs 4 ounces, two-year warranty
Film from American Paper Optics
Pros
- ISO 12312-2:2015(E) certification is verifiable on paper
- Hook-and-loop straps give a genuinely secure objective fit
- Scratch-resistant film from a NASA and AAS recommended supplier
- Backed by a two-year Celestron warranty
Cons
- Only fits Celestron 8 inch Schmidt-Cassegrain and EdgeHD tubes
- Costs considerably more than generic film for the same job
This is the most formally certified product in the roundup. It conforms to the ISO 12312-2:2015(E) international safety standard for filters used for directly viewing the Sun, and the solar film is produced in the USA by American Paper Optics, independently tested by a third-party lab. That supplier is named on published lists of recommended suppliers by NASA and the American Astronomical Society, which is the kind of provenance that matters in a category where a bad filter is a permanent eye injury.
The retention system is the other thing that separates it from a sheet. Two hook-and-loop straps hold the filter against the telescope objective, so it stays on without tape and without a clamp screw. For visual observing and imaging, the orange tint gives a natural look that many people find easier to work with than a neutral white disc.
With 597 reviews at 4.5 stars and 76 percent five-star ratings, buyers consistently praise the film quality, the secure strap fit and the natural orange view. The small minority reporting issues tend to fall into two groups: those whose telescope is not a Celestron 8-inch SCT, and a few who found the coating or the fit less kind than expected.
We like that the warranty is two years and that support is based in the US. For a purchase you are making once and then trusting with your eyesight, that matters more than a marginal difference in image contrast.
When this is the right filter
If your telescope is a Celestron 8-inch Schmidt-Cassegrain or EdgeHD, this is the straightforward answer. The fit is designed for that tube, the retention is mechanical, and the certification is documented. You are not cutting anything, and you are not relying on tape.
It also suits anyone who wants a documented safety standard rather than a manufacturer’s assertion that their film is safe. The compliance claim on this model is specific, dated and testable.
When it will not work for you
It will not fit anything else. Not a different Celestron model, not a refractor, not a Dobsonian, not a camera lens. That single-instrument limitation is the whole reason it does not sit at the top of this roundup despite the strongest certification here.
You also pay a premium for the fit and the certification, and generic certified film in a bare sheet costs a fraction of it. If you are comfortable mounting your own filter, the money buys convenience rather than safety.
4. Celestron EclipSmart Universal Solar Filter: One Filter for Scopes, Spotting Scopes and Cameras
Celestron EclipSmart Universal Solar Filter for Telescopes
ISO 12312-2:2015(E) compliant
Adjustable fit from 75mm to 100mm outer diameter
Folds flat into a reusable bag
Also suits DSLR lenses
Pros
- One adjustable filter covers a wide range of tube diameters
- ISO 12312-2 compliant film from American Paper Optics
- Folds flat and stores in a reusable bag
- Works across telescopes spotting scopes and cameras
Cons
- Fit range stops at 100mm so larger front cells are out of reach
- Paper-based construction is less durable than an aluminium cell
- Lowest average rating in the roundup at 4.2 with a visible share of one-star reviews
This solves a specific problem: not knowing exactly what diameter you need before you buy. Adjustable side panels let the filter expand across a range from 75mm to 100mm in outside diameter, and an elastic band secures it. If you have a small refractor, a spotting scope and a DSLR with a 58mm-to-77mm lens thread, one filter can cover all three.
The certification is the same standard as the 8-inch model, with film from American Paper Optics and independent third-party testing. That puts it on equal footing with the premium Celestron filter even though the construction is simpler.
What makes this the most bought product in the roundup by category rank is exactly that flexibility. But the review profile is more divided than the rank suggests. At 4.2 stars across 452 reviews, with 62 percent five-star but 6 percent one-star and 6 percent two-star, there is a real minority who did not get on with it.
Reading those reviews, the complaints cluster around sizing and durability. Some buyers found the adjustable panels did not grip a tube as tightly as they expected, and paper-based construction does not survive being crushed in a bag the way an aluminium cell does.
What to check before you order
Measure the outside diameter of your tube or lens barrel, not the clear aperture and not the nominal aperture. A 90mm refractor often has an outer cell diameter somewhere between 94mm and 100mm, which is exactly the kind of number that decides whether the adjustable panels reach.
Then set the panels snug and test the elastic band before you point the thing at anything. If the filter can be twisted by hand with the band attached, it is not tight enough.
Where it falls short
One hundred millimetres is a hard ceiling. If your instrument is larger than that, this filter is simply the wrong object, and no amount of adjustment will change that. Dobsonian owners with big front cells should look at a cut-to-size sheet instead.
It is also the least durable format here. Paper-based construction with side panels is fine for occasional use and awkward for regular solar work.
5. Thousand Oaks 12×12 Solar Filter Sheet: Best for Large Apertures and Multi-Instrument Kits
Thousand Oaks Optical BP-12 12 inchx12 inch Solar Filter Sheet for Telescopes, Binoculars and Cameras
12 x 12 inch orange sheet
Model BP-12, weighs 200 grams
Flat surface with no wrinkles
Also fits finders, binoculars and eclipse viewers
Pros
- Highest-rated product in the roundup at 4.7 stars
- Flat polymer surface avoids the wrinkles common in thin film
- One piece covers a large front cell or several instruments
- Made in the USA
Cons
- Arrives in cardboard with no storage case
- Requires the user to cut and mount the sheet
This is the highest-rated product in the whole roundup, at 4.7 stars across 437 reviews with 86 percent five-star ratings and only 1 percent one-star. The reason for that score is simple and physical: the surface is flat. Wrinkles and creases are the norm in thin film solar filters, and every one of them scatters light and distorts the image. This polymer sheet is described as having a flat surface by comparison, and observers notice the difference in spot contrast immediately.
At 12 by 12 inches, this is the largest sheet in the range here. One piece will cover a 10-inch or 12-inch Dobsonian front cell with room to spare for taping, and the remainder can be cut down for finders, binoculars, a camera or a pocket eclipse viewer. It is the most versatile single purchase in this roundup if you own more than one daylight-capable instrument.
Reviews describe a flat, wrinkle-free surface and good contrast for sunspot and granulation work, which is the strongest consensus anywhere in this set. The maker also repeats the reminder that matters most: do not see the Sun through an unprotected sight block, and remove or cover your finder if it is not protected. That single sentence prevents the most common accident in solar observing, which is not forgetting the main filter but leaving the finder open.
One practical warning. The sheet comes in a cardboard wrap and does not include a storage case. Interleave the film with clean flat card or mount it immediately, because a crease once taken is permanent and no amount of careful handling later will remove it.
What to check before you mount it
Because this is the largest sheet and the flattest, it is the most forgiving to work with. Lay it flat on a clean table, mark your cut line from a paper template, and cut in a single smooth stroke. Hold the cut piece up to a bright window and reject any piece that shows pinpoints of light.
Mount it to the front cell with the sun-facing side clearly marked, and re-check the attachment every time you move the telescope. A filter that has shifted by a few millimetres is a filter that is no longer covering the beam.
Where it is the wrong choice
If you want something that clamps on by itself, this does not do that. It is a material, not a product, and the mounting work is yours. It is also heavy at 200 grams, which is irrelevant on a large Dobsonian and awkward on a small travel scope.
It is also white light only. No sheet in this roundup shows you prominences.
6. Celestron EclipSmart Filter for 127mm and 130mm Reflectors: Best for Small Reflectors
Celestron EclipSmart Telescope Solar Filter for 127mm & 130mm Reflectors
ISO 12312-2:2015(E) compliant
Fits named Celestron 127mm and 130mm reflectors
Weighs 3.04 ounces
Straps plus a protective safety cap
Pros
- ISO 12312-2 compliant film with a protective safety cap
- Snug hook-and-loop attachment that owners report fits well
- Users report good solar views and successful eclipse imaging
- Build quality described as very good for the money
Cons
- Clear aperture is smaller than the frame so centring the Sun takes longer
- Limited to a specific list of Celestron reflector models
This one exists because small Celestron reflectors are among the most common beginner telescopes, and their front cells do not take a generic ring. It fits a named list including the PowerSeeker 127EQ, NexStar 130SLT, Astro Fi 130, Omni XLT AZ 130, SkyProdigy 130, and the StarSense Explorer LT 127AZ and DX 130AZ.
The retention is two hook-and-loop straps, and there is a detail worth crediting: a safety cap that protects the outer surface of the film when the filter is not in use. On any front-mounted filter, the most likely point of damage is the exposed face, and a cap means it is covered while the filter sits in a case or on a table.
Across 156 reviews at 4.6 stars with 77 percent five-star, the feedback centres on a secure fit, good value and genuinely good solar images. Owners report success with eclipse viewing and with sunspot imaging, which suggests the transmission is well judged for both visual and camera work.
The recurring criticism is about the clear aperture. It is smaller than the surrounding frame, which means the usable beam is narrower and finding and holding the Sun takes longer than it would with a wider filter. It is a mild inconvenience rather than a safety issue, and it disappears once you learn the offset between your finder and the main tube.
Who should buy this one
Owners of the listed Celestron 127mm and 130mm reflectors who want a factory fit with documented certification and no cutting. It is also a good choice for anyone planning to shoot the Sun with a camera, because the film is stated to work for imaging as well as visual observing.
If you have one of these telescopes and plan to use it for anything else afterwards, buy the cap and treat it gently. That is the whole maintenance routine.
Who should skip it
Anyone whose telescope is not on the list, including Celestron owners with other apertures or other brands with the same nominal size. The fit is model-specific and will not generalise.
And if you find and centre the Sun frustratingly, note that the small clear aperture is the reason. Observers who prioritise easy acquisition over everything else should look at a wider filter.
7. Astromania Deluxe Filter 100mm: Best for a Rigid Aluminium Cell
Astromania Deluxe Filter 100mm Adjustable Metal Cap for Telescope Tubes with Outer Diameter from 70mm to 92mm Aperture 75mm
Anodised aluminium cell, 100mm outer diameter
75mm inside diameter
Fits 70mm to 92mm tubes
ISO 12312-2:2015 compliant
Pros
- Only filter here with a rigid anodised aluminium cell
- Three clamping screws give a genuinely secure fit
- Clear white-light rendering rather than the usual dull orange
- Baader Astro film in a sturdy cell
Cons
- Film is exposed inside the ring so a scratch or puncture ruins it
- Stated 70mm to 92mm range leaves gaps and some 92mm tubes will not fit
- Clamping screws are described as overlong and awkward
- Some units arrive scratched or with doubled film that must be cut away
This is the only genuinely rigid filter cell in the roundup. The anodised aluminium housing will not flex, will not crease and will not compress in a bag, and it holds Baader Astro white-light film in a fixed aperture. Three clamping screws with protective plastic caps grip the tube without marking it.
The image is the other reason people choose it. Instead of the orange rendering that most film filters produce, this one gives a clear white-light view, and reviewers describe the result as sharp and free of aberration. White balance behaves predictably too, which matters if you are photographing rather than looking.
This is also the most polarised product here. At 4.1 stars across 130 reviews, with 62 percent five-star but 9 percent one-star and 9 percent two-star, the enthusiasm and the complaints are both loud. Enthusiasts love the cell and the image. Safety-conscious reviewers raise concerns about the film being exposed inside the ring with no protective glass, about fit confusion right at the 92mm boundary, and about units arriving scratched or with adhesive residue.
We think the exposure point is the one to weigh most heavily. Aluminium protects the film from bending and creasing, but it does not protect it from a fingernail, a tool or a sharp edge. Handle it face-up on a soft surface and store it in a case.
Measuring matters more here than anywhere else
The inside diameter is 75mm and the outside is 100mm, and the manufacturer states it suits tubes with an outer diameter of 70mm to 92mm. Measure your tube before you order, because some buyers report that a nominal 92mm tube will not actually go on, and the boundary cases are where returns happen.
Also check the film on arrival. The maker notes that some units may show a wavy line in the film because of the larger diameter, and states that this does not affect observation. Scratches or a doubled layer of film are a different matter. The maker’s own instruction is blunt: never use your telescope if the filter is in any disrepair.
Where it falls short
The clamping screws are widely described as overlong and awkward to use, and some users report improvising a better fix with hook-and-loop straps. That is a fair criticism of an otherwise well-built object.
There is also the fit ceiling. Above 92mm outer diameter, this cell does not apply, and you are back to cutting your own film.
8. Rainbow Symphony 70mm Solar Filter: The Best Value for Smaller Tubes
Rainbow Symphony Solar Filter 70mm Black Polymer
70mm black polymer white-light filter
Slip-fit cell, weighs 18.14 grams
Adhesive felt strips included
Also made in 50mm 60mm 76mm and 101mm
Pros
- Buyers repeatedly praise the natural orange rendering and clear sunspot detail
- Works on binoculars
- finders and camera lenses too
- Included felt strips can be trimmed for a snug fit
- Brand appears on published lists of tested solar filter makers
Cons
- Cardboard rim is not rigid and may not grip a tube out of the box
- Size labelling can mislead since some 70mm versions do not fit a nominal 70mm telescope
- Only one filter per purchase so binocular pairs need two
- Highest share of one-star reviews here at 9 percent
The Rainbow Symphony filter is the simplest finished object in the roundup. Black polymer film sits in a slip-fit cardboard cell that goes over the front of the instrument, and a pack of adhesive felt strips lets you trim the rim to fit your tube. At 18 grams it weighs almost nothing, which makes it easy to carry to several instruments on the same outing.
Rainbow Symphony appears on published lists of tested solar filter brands, and the image is what you would expect from good white-light film. The Sun comes through in a natural orange tint with sunspots clearly visible, which is the classic introductory solar view.
At 4.2 stars across 115 reviews, with 65 percent five-star but 9 percent one-star, this has the highest share of one-star reviews in the roundup. The critical reviews concentrate on the flimsy cardboard rim and on size labels that do not match real tube diameters. Measuring the outer diameter before ordering is the advice that appears over and over.
The one-star reviews also include concerns about how much light the film attenuates, which is a fair thing to ask about. Treat it as a white-light solar filter and judge it as one. It is not an H-alpha product and will not reveal prominences.
Getting a secure fit out of a cardboard cell
The felt strips are the whole trick. Trim them to the inside of the cell so the cell sits tight against the tube wall with no wobble, then check the fit by gripping the cell and trying to twist it. If it turns at all, add another strip. Two thin strips beat one thick one because they put pressure on two opposite sides rather than pushing the cell off-axis.
The same advice applies to the size question. If you have a nominal 70mm scope, measure the actual outer diameter of the tube before ordering, because the labelling is where most of the disappointment comes from. Other sizes are offered at 50mm, 60mm, 76mm and 101mm.
Who should pick this one
Observers with a small instrument who want a ready-made filter without cutting anything, and who will spend two minutes trimming felt for a proper fit. It also works across binoculars, finder scopes and camera lenses, which makes it a good portable option for outreach work.
Only one filter is included per purchase, so if you want to filter a binocular pair you need two.
Who should pick something else
Anyone who knocks their equipment about. A cardboard rim will not survive being dropped repeatedly, and the exposed film inside will crease if the cell flexes. For regular solar work, a rigid aluminium cell or a factory strap-and-cell filter is a better long-term buy.
And if you plan to shoot the Sun rather than just look, remember that orange film shifts white balance and reviewers report having to work around it.
How to Choose a Solar Filter for Your Telescope
Most wrong purchases in this category are sizing mistakes, not quality mistakes. Get the measurement right and almost any certified filter in this roundup will serve you well.
How to measure your aperture and match the cell size
Measure the outside diameter of the front cell, not the aperture and not the number printed on the tube. This is the single most important number when buying a filter, and it is the one most people guess at. Use a caliper if you have one, or a ruler held against the cell with the telescope on level ground.
Measure the outside diameter of the front cell or dew shield in millimetres.
Add roughly 10mm to 25mm of extra diameter so the filter overlaps the cell all the way round.
Match that figure against the fit range in the product listing, not against the nominal aperture.
If the range does not cover your figure, cut a sheet to size rather than forcing a ring that does not fit.
Aperture and cell diameter are frequently different numbers, and a 90mm refractor can have a front cell anywhere from roughly 94mm to over 100mm across. Filters specified by outer diameter are the ones to compare against, which is why the Astromania’s stated 70mm to 92mm tube range and the Celestron universal’s 75mm to 100mm range both describe the tube, not the clear opening.
Film or glass, and what optical density means
Every filter in this roundup is aluminized or black polymer film, and that is not a compromise. Both film and glass filters work by cutting the Sun’s visible and infrared energy to a safe level before it enters the telescope, and film has two real advantages: it is far lighter, and it costs a fraction as much. Glass is heavier and pricier but survives rough handling.
Optical density is the log scale of that light reduction. OD5 means a reduction of about 100,000 to 1, which is the working range for visual solar observing. More density is not automatically better, and this is a genuine point of confusion. Over-reduction makes the image dim, and a dim image hides the faint detail you bought the filter to see. If you are photographing, reviewers regularly report that a filter was darker than expected and that white balance struggled as a result.
Why ISO 12312-2 matters and what uncertified stock actually is
ISO 12312-2:2015 is the international standard for filters used for directly viewing the Sun. Four of the eight filters here state compliance with it, including the Astromania cell, which also uses Baader Astro film and claims to block 99.9 percent of incoming light.
The uncertified alternative is a large part of the search results for this topic, and the difference matters more than any other single factor in this guide. An uncertified filter sold without a stated optical density is a piece of tinted plastic of unknown density sold in a market where the cheapest option is heavily promoted. We do not use one and we do not recommend one. Price is never a safety margin.
Two further rules follow from the same logic. First, if a filter is torn, creased, scratched or punctured, retire it rather than repairing it. Second, if a filter is offered at an unusually low price with no manufacturer name and no certification, the bargain is in the product, not just the price.
Finding the Sun without a finderscope
Your finder will destroy your eye if it is unfiltered, and it will damage its own optics too. The correct procedure is short.
Remove the finderscope entirely, or cover its front lens with the supplied cap or with an opaque material such as gaffer tape.
Fit your certified filter over the front aperture of the main tube and confirm it is secure.
Point the main tube roughly at the Sun by shadow or by using the date and time on an ephemeris app.
Sweep slowly until you find the bright disc, then fine-tune with small finder movements until the Sun is centred and steady.
On a Dobsonian or a Newtonian, cap or remove the finder rather than filtering it. On a refractor, a filtered finder is acceptable, but removing it is simpler and eliminates the risk entirely. This procedure is worth knowing before you need it, because finding a filter-free Sun on the first attempt is not something to attempt.
A pre-use pinhole check and how to store the filter
Film fails by pinholing, and pinholes arrive through handling rather than age. Two minutes of inspection before every session prevents the single worst outcome in solar observing.
Hold the filter up to a bright lamp or a sunlit window and look for any pinpoint of light.
Check the rim and the mounting face for tears, creases and lifted edges.
Confirm the filter still covers the full beam by checking that no clear glass is visible around the edge when fitted.
Confirm the retention is tight by trying to rotate or lift the filter once the telescope is pointed near the Sun, never at it.
Between uses, store film flat between clean cards. Do not roll it, do not leave it in a car, and keep it away from anything dusty or sharp. The largest sheet here comes in a cardboard wrap with no case, so making your own flat storage immediately is worthwhile.
Solar eclipses and photographing the Sun
For a partial eclipse, the same rule applies as on any ordinary solar day: a certified telescope filter, front-mounted, sized to your aperture. For a total eclipse, once the photosphere is fully covered, the filter comes off and you get the corona, but the instant of second contact needs a certified filter of the correct density. People have damaged vision by removing the filter a few seconds early or late. Treat the transition as a timed step, not a judgement call.
For solar photography, mount the camera behind the telescope or a telephoto lens with the filter over the front of the lens, never over the sensor. Reviewers who shoot the Sun report two recurring problems: white balance failure with orange film, and an optical density higher than expected. Shooting in manual rather than auto white balance solves most of the first.
One note for anyone setting up for an eclipse away from home: a wide-brimmed hat and sun shirts make a longer observing session survivable. Our picks for a packable sun hat and for UPF sun shirts are built for exactly that kind of all-day daylight exposure.
H-alpha filters and solar wedges are a different category
Nothing in this roundup shows you prominences, filaments or the chromosphere, because those features require narrowband light at 656.3nm. As one Cloudy Nights discussion put it, H-alpha solar astronomy uses etalons, not plain filters that you screw in the eyepiece, and the safest bet for H-alpha solar is a dedicated solar telescope.
A wedge or Herschel-style arrangement places the etalon inside a refractor’s optical train, which is why a dedicated solar telescope is the safer architecture. A thread-on eyepiece H-alpha filter is a different instrument from anything reviewed here, and you should not treat a white-light sheet as a substitute for one.
Jupiter and Moon filters are also a different category
Planetary colour filters and neutral density Moon filters answer entirely different questions from a solar filter. They do not reduce sunlight to a safe level, and putting one over the front of a telescope while pointing at the Sun would do nothing useful. A neutral density Moon filter is for the Moon. A colour filter for Jupiter is for contrast on the belts and zones at night. Neither substitutes for a solar filter, and neither belongs on the front aperture in daylight.
For the rest of your optical train, our guide to the best telescope eyepieces for planetary viewing covers the eyepieces that pair well with solar work, since low-power wide-field eyepieces make finding and centring the Sun far easier.
Frequently Asked Questions
What filter do you need to look at the sun with a telescope?
You need a certified solar filter that mounts over the front aperture of the telescope, such as aluminized polyester film in a cell meeting ISO 12312-2, or nickel-chromium coated glass. The filter must cover the entire front opening before sunlight enters the optics. Never use an eyepiece-mounted solar filter, and never use eclipse glasses on a telescope, because magnification concentrates sunlight far beyond what they are designed to block.
What is the best solar filter for a telescope?
The best solar filter for most telescopes is a white-light filter meeting ISO 12312-2 that covers the front aperture completely. Our top pick is the Thousand Oaks 6×6 black polymer sheet, the most reviewed filter in our testing, with 1097 reviews at 4.6 stars. Telescope owners wanting a factory cell rather than a sheet should choose a rigid metal cell sized to their front cell diameter.
Is it safe to look at the Sun through a telescope?
Only with a proper front-mounted solar filter fitted and verified. Concentrated sunlight can cause permanent retinal damage in a fraction of a second, and it can also burn the diagonal, the eyepiece and other optics in the path. Many observers suffer eye injuries each solar season. Cover or remove the finderscope, fit a certified filter over the front aperture, and never look at the Sun without it.
What happens if you look at the Sun through a telescope without a solar filter?
The concentrated sunlight is focused directly onto the retina, causing permanent damage or blindness, often within a fraction of a second. The injury is painless at the moment it happens, so the damage is not noticed until later. Your telescope is also at risk: the front lens, corrector plate, diagonal and eyepiece coatings are rated for starlight, not for the Sun, and can be permanently ruined in minutes.
What type of telescope is best for viewing the Sun?
Any telescope works for white-light sunspot viewing with a correctly sized front filter. Refractors and Schmidt-Cassegrains are easiest because their front cells are fixed and easy to measure. Dobsonians give the largest, brightest images but have larger front cells that need a bigger filter. For seeing prominences and the chromosphere rather than sunspots, a dedicated solar telescope is the right instrument.
What lens filter do I need for a solar eclipse?
For any partial phase of a solar eclipse, you need an ISO 12312-2 certified solar filter rated for telescope use, mounted at the front of the aperture or lens. Eclipse glasses are safe for the naked eye only and cannot be attached to a telescope. During totality the photosphere is covered and the filter can be removed to see the corona, but you must put it back for the final partial phases on either side.
Which Solar Filter to Buy First
If you want one product that solves white-light solar viewing for almost any instrument, take the Thousand Oaks 6×6 black polymer sheet. It carries 1097 reviews at 4.6 stars, it costs less than any finished cell in this roundup, and its cut-to-size format means no sizing guesswork. Buy the 8×8 inch version instead if your front cell is large, and the 12×12 inch if you want a flat surface and several instruments from one sheet.
If you would rather have hardware retention and a documented certification than cut and tape your own, choose the factory cell that matches your tube. The Celestron EclipSmart models cover specific Celestron apertures with hook-and-loop straps and ISO 12312-2:2015(E) compliance, and the Astromania 100mm cap is the only rigid aluminium cell here, which makes it the most forgiving option if you transport equipment in a car.
Measure your front cell’s outside diameter before you order anything, trim the felt strips on the budget Rainbow Symphony cell so it cannot be twisted, and run the pinhole check every single time. Whatever you choose among the best solar filters for telescope sun viewing, it goes on the front aperture, it covers the entire beam, and it is never replaced by eclipse glasses.
While you are out in daylight for a long session, our guides to the best packable sun hats and the best beach sun shelters cover the parts of solar observing that happen away from the eyepiece.