FAQ – Frequently Asked Questions

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I want to take images of the sun. Do I need AstroSolar® 5.0 or 3.8 Film?

In short, you can use the visual version of the filter (AstroSolar® Safety OD 5.0)without any problems for prime-focus photography with a DSLR. You need the photographic version (AstroSolar® PHOTO OD 3.8) only for higher magnifications, e.g. if you use eyepiece projection to achieve high magnifications and to capture details on the sun with video cameras.

Single Images, Images of the complete Sun an Focal Photography: AstroSolar® Safety Film (OD 5.0)
If you use a camera which is attached directly to the telescope (in the prime focus), without eyepiece or camera lens, then AstroSolar® Safety Film (OD 5.0) is perfect for you. Then, you also don’t need to worry about looking into the sun through the camera’s viewfinder, and a modern digital camera will achieve exposure times which are so short that they will freeze the seeing. As a general rule, you should always use the display / live view of your camera and never the optical viewfinder, if you are working with the OD 3.8 film – with Safety Film OD 5.0 you can also use the viewfinder.
The solar granulation can be captured even with 600mm of focal length, although a good location (clear, transparent sky) and some image manipulation for enhancing the contrast are really helpfull. The aperture is as important as the focal length, because it defines the resolution of the telescope. A good lens telescope with 80-100 mm aperture is enough. But to see these structures clearly, you should use focals lengths of 1500-2000mm and at least an aperture of 125-150mm – then you have a focal ratio of about f/10, which allows for sufficently short exposure times with a DSLR and Safety Film OD 5.0. But don’t forget that these are only aproximate values, which also depend on the resolution of your camera – that is, the pixel size. The focal length which is necessary to project the whole sun onto the sensor depends on the sensor size – as a rule of thumb, the sun appears ca. 1 cm large for each meter of focal length.

Eyepiece Projection (Afocal Photography) and Lucky Imaging with video cameras: Photographic Film (OD 3.8)
You can reach higher magnifications with eyepiece projection. For this, you need either slim 1¼”-eyepieces and an adapter for projection, or – better – eyepieces with a thread close to the eye-lens like our Hyperion 68° or Morpheus 76° eyepieces. You can find many possible ways for attaching a camera in the Hyperion PDF. Formulas for calculating the resulting focal lengths (sorry, so far only in German) can be found on the description of our OPFA – Ocular Projection and Focal Adapter.

You can reach extreme focal lengths easily with eyepiece projection – thus, the image will get too dark, and you need the photographic film to achieve short exposure times. The seeing will be more prominent, too, so it is better to take many images instead of single shots. For this, you need a video module, so that you can select and process only the best images – this is called “Lucky Imaging”.

So, you can usually take the Visual Safety Film (ND5.0) also for photography, als long as you don’t take solar photography to the extreme.

Solar Viewers

How long can I use Solar Viewers?

If the SolarViewers are handled with care, they will last for a long time – most probably much longer than we can state publicly. Official certificates are not valid for infinity – otherwise, we would have to commission very expensive long-term tests – and nobody can give us a warranty for having stored his viewer properly. This is the reason why we can’t advertize on our website that you can use the film for decades if you handle it with care. This is somehow the same problem as with canned food: A carefully sterilised can of food will last for up to 50 years without even changing its taste – but nobody will (may) write this on a can…

At least, we ourselves still store some SolarViewers from 1999 here which we still use for a quick look at the sun to see what’s going on there. We were surprised and happy to see how many people called us in the last days before the last german-eclipse in March 2015 and wanted to know if they can still use their SolarViewers they kept from back in 1999. That was 16 years ago and shows us, how much people valued the memory of that event.

Our answer (in March 2015) was always the same:
If there are no obvious scratches or damages showing up when holding the viewer towards the sun and if the sun does not appear to be inconveniently bright, then the film most probably is still fine and you can use it – but unfortunately we cannot take over a warranty. Please note that the newest standards say that you are to take a break after every three minutes of observation. We concur with that.

UPDATE: Since the DIN Norm changed in 2015 and our old viewers don’t reach the latest norm anymore, we can’t legally recommend to use them anymore. We advise everyone to purchase our ISO 12312-2:2015 compliant Solar Viewer AstroSolar Silver/Gold. Those are certified as safe and can be stored indefinitely according to the DIN norm which is quoted on the official AAS website (see quote below):

Quote by Rick Fienberg, AAS Press Officer:
Some eclipse glasses and solar viewers, even new ones, are printed with warnings stating that you shouldn’t look through them for more than 3 minutes at a time and that you should discard them if they are more than 3 years old. Such warnings are outdated and do not apply to eclipse viewers compliant with the ISO 12312-2 international safety standard, which was adopted in 2015. If your eclipse glasses or viewers are relatively new and are ISO 12312-2 compliant, you may look at the uneclipsed or partially eclipsed Sun through them for as long as you wish. Furthermore, if the filters aren’t scratched, punctured, or torn, you may reuse them indefinitely.

The film on my Solar Viewers has a slight bend. Does this affect my security?

Detailed question:

The film in my AstroSolar® Solar Viewers has a slight bend on one eye. Can I still use the Solar Viewers appropriately ?

Answer: It might be a mark created from the handles. If you look through the Solar Viewers and do not see any white spots, then using them to observe is clompletely safe.
Even a scratch or a damaged spot (less than 0.5 mm), still does not represent a real threat. It is for this reason the film is coated on both sides – to offer the maximum protecion even if one side is damadged.

For how long can I look at the Sun using Baader solar viewer?

We recommend that with any viewer you shouldn’t look at the Sun for more than 3 minutes. Before you look again take 5-10 minutes rest and check if you have any vision problems. This way, you can detect any latent eye disease. For example if even after two hours of observation you still see the silhouette of the Sun, you should visit an ophthalmologist, because a previously undiscovered retina problem might exist.

Can eyes get damaged even with the solar viewers on?

All ISO DIN 12312-2:2015 compliant Solar Viewers provide a safe viewing of the Sun.

We have been using the AstroSolar® Silver filter material for our solar viewers for more than 25 years. More than 23 million people have used them, mostly during partial eclipses and no eye damage has come to our attention. Recently the ISO norm has changed and our former AstroSolar Silver viewers (that were certified as safe for 25 years) didn’t reach it by an ever so tiny percentage. For this reason we developed our Solar Viewer AstroSolar Silver/Gold with eyesided reflex-free viewing which are compliant to the latest norm and was used by many customers for the 2017 American Eclipse.

If you have the feeling of a blurred vision or if even after two hours of observation you still see the silhouette of the Sun, you should visit an ophthalmologist, because a previously undiscovered retina problem that has been luring in the background for longer time (such as the very beginning of a process that might lead to a loose retina) might exist. In these cases the condition has nothing to do with the security of the viewer (Baader viewers are absolutely safe and will stand any test) – but the excitement and the concentration during the event may have triggered something that was there already. This is not uncommon and people have found that the eclipse had helped to notice an eye-problem before it became a catastrophe.

We are glad that in the past we haven’t had a single report of an eye damage due to our solar viewers.

For the safest solar viewing experience, you should make sure before using our viewers that no prior eye disease, no eye hypersensitivity or retina phototoxic reaction occurred.

For more read: Differences in AstroSolar® film


Are solar viewer sun goggles with Baader AstroSolar® silver film suitable for children?

Our CE-certified solar viewers offer protection and safe observation, keeping in mind that the observation should be done in 3 minutes intervals with a longer rest period between. Our products come with the notice: “Not suitable for children under 14 years” for legal reasons. The risk is higher, especially when you leave the children alone with such products. Solar observations should always be done under adult supervision.

We believe that the children should be thoroughly informed and forced to use eye protection in every case. The only serious eye damage (retina burn) we have encountered during these years of solar eclipses observations comes from a childish dare: Whoever looks directly at the Sun, without blinking, suppressing his involuntary protecting reflex, and most importantly WITHOUT solar viewers, wins.

The worst with that “challenge” is that after a few seconds, the strong urge to look away fades. Then the light sensitive pigment, rhodopsin, responsible for converting light into electrical signals, gets destroyed.

A person in such condition can look directly at the sun without unease. Since there are no pain receptors in the retina, he doesn’t notice the retina getting burned exactly where the vision is sharpest. In an optical examination, someone will clearly see the burned retina, which in case of partial eclipses will have a distinct dark crescent shape.

These subjects have the same visual sensitivity as individuals with macular degeneration. Right in the middle of the field of view, in the point we instinctively use to focus or vision, will be a dark spot that will never disappear.

A solar eclipse, even a partial one, is one of the most important and impressive events, which can arise a great interest in environment and maybe later in natural sciences. The use of proper protective measures should be strictly practiced and this will raise the interest in astronomy.

AstroSolar Film

Can I stretch the film between 2 Plexiglas panels for better protection?

Question in Detail:
Can I stretch the film between 2 Plexiglas panes? (5mm each) The two panes are then placed in a plywood frame. (several 10mm layers glued on top of each other) I put the whole thing over my Bresser 8″.
I mainly want to protect the foil from contact and damage. Whether this makes sense optically or photographically – no idea.

Answer: technically this is of course possible – but even if you could find planeoptically polished Plexiglas of the highest optical quality, the picture would be much worse than without it..

On the one hand, the film is designed to sit loosely. If it is put under tension, the contrast drops. This is also the reason why we offer our ASTF filters with temperature compensated filter holders: If you glue the film e.g. into a black frame (as is often done with cheap holders) and this cheap holder heats up during observation, the image will also deteriorate during longer observation and become „muddy“. Of course, then the film will be blamed and not the frame.

And on the other hand one does not observe (hopefully) through the closed windows of an apartment… the effect would be the same: a muddy sun as a white ball without structure..

To find two planeoptically polished Plexiglas panes without wedge errors (i.e. with exactly parallel surfaces) and to mount them perfectly parallel is an impossibility. This is because flat surfaces are harder to produce than sphere/parabolic mirrors. Each such Plexi precision disk would be more expensive than the mirror of your telescope.

Our many years of experience have shown that if you store the film filter in a dustproof and moisture-protected cardboard box, it can be used for many years. As long as the film is not processed with pointed objects, the film coated on both sides is surprisingly robust. If you install it in a slightly wider frame, you can handle the sun filter well without worrying about accidentally touching the coated film.

Therefore we can only advise you to use the film as it is and to avoid any additional „protective layer“.

Can I laminate AstroSolar® Film for better handling?

Question in Detail:
I am looking for solar film (sheets) which I would like to laminate onto clear plastic (PMMA or PC) sheets and lasercut into discs. It will be used to look directly into the sun through the discs. Is it possible to laminate the solar film and to lasercut it? As an alternative should it not be possible, I would like to ask if it would be a problem if the film is placed in between two discs of clear plastic?

AstroSolar® Film cannot be laminated as the process-tension may damage the metal coatings and lead to “tension-cracks”. We do NOT recommend this procedure. The danger of damaging the metal coating of AstroSolar® Film while laminating however is not the only reason, why we do not recommend such procedure.
ANY additional layer before/after our film (be it lamination or discs of clear plastic) will dramatically reduce the optical quality and thus the observation experience. The two additional layers of plastic would create heavy stray light which would make the solar disc appear unsharp. It would also create blooming effects that would prevent you from seeing any details such as sunspots or granulation on the sun.

We don´t know for what purpose you are trying to do this, but if you are looking for a ready-to-go solution, please take a look at our Baader Solar Filters.

Is there a safety risk if the AstroSolar® film is stretched too tight?

Detailed question:

I have constructed a lot of solar filters using your AstroSolar® film. I have always used the system with 2 cardboard rolls. Recently I tried the system described with the film with two cardboard rings and additional PVA glue near the edges (1 cm) of the bi-adhesive film. For that I’ve used a very stiff cardboard. When the glue dried, the film was stretched almost wrinkle-free. Only around the edges there is still a small wave. Is this a safety risk (if the film isn’t wavy), or is that something merely optical, so the picture won’t be as perfect as it could be (that’s no problem for me)? Please advise if the filter is risky to use, or can I use this filter without hesitation?


Answer: If the film is stretched, that makes no real security concern. It only affects the image quality. At magnifications higher than 60 times, this doesn’t allow focusing and will increase the blur. Therefore we recommend for those who make their own filters to drop the cardboard film holder on top of the film so it remains relaxed and slightly wavy.

Since the optical performance is not important to you, and since you can’t break it apart because of the PVA glue, you can use your mounted filter without any concerns. We recommend the method you described to construct a filter, especially avoiding a metal frame, so that the extensive tension won’t be a problem as the cardboard is more flexible and won’t let the film tear apart.

Where we don’t want to see such tension is when using metal frames for the film holder. Thermal expansion could create more tension and since the film is definitely not stronger than the metal frame, it would break. That is the reason why we decided to produce our own filters after 15 years.

What should I consider before I use the AstroSolar® film?

Our AstroSolar® film ALWAYS comes between one paper and transparent OR white plastic sheet.

This material should eventually be removed, to take advantage of the full optical quality of our filter. These layers protect the film during transport and help us cut and fit it in its sockets. This is also written in the product manual.

Each additional transparent film (or glass plate) reduces the optical quality and the images quality taken with AstroSolar® film.

Can I use a grey filter (neutral density filter) to observe the Sun?

Gray filters or neutral density filters should NEVER be used IN FRONT of the objective, without any additional filter (such as AstroSolar® or other sun filters).
There is a risk that the filter gets very hot and shatters unexpectedly.

Can I use the AstroSolar® safety film OD 5.0 to take pictures of the Sun in the infrared region?

Unfortunately AstroSolar® safety film is not designed for IR-photography. It would not damage your camera sensor, but there is an interference, which might cause double-images.

Baader Solar Filters

My ASTF-filter shows tension lines – do I need to have it replaced?

Solar filter Close Up

These are by no means “tension lines”.  Much to the contrary – this image is the clear proof that we do not at all put the film under tension when mounting it!
These “ripples” (if you want) are inevitable to appear during the production process, because during all the several steps that the film must be subjected to, it is totally forbidden to stretch it in any way. Exactly this stretching would destroy the optical quality (= absence from astigmatism) once and for all.
All too many users who buy our film (most of all the Chinese offerings of extremely cheap cell mounted solar filters) do overstretch the poor film as if they want to produce a drum. This does “look” wonderful indeed if you look at the product, but the quality of solar details looks awful when you look through such a “drum-filter”…

The filter does not need to be flat like a high-end glass filter, but it must be free from tension. This can only be the case when it can “work” in the filter cell. If the film is glued e.g. into simple a black plastic cell, the cell will get warmer in the sun, expand and stretch film – so that the image will get blurry and without contrast. That’s why we mount the film for telescopes, which use higher magnifications, in temperature-compensating ASTF filter cells.

On the other hand, a good glass filter in front of the telescope needs the same optical precision as the lens of the telescope, and would be in a similar price range as our D-ERF pre-filters which are used only in combination with H-alpha-filters. The nice and cheap glass filters are more in the quality range of window glass instead of optical lenses…

So again – if we were to “flatten out these ripples” by stretching them flat, then indeed you would complain about “blurry image above 60-times magnification” – just as it is seen when buying a “precision glass solar filter” (meaning: the affordable “window-glass” filters).

What can I do about reflections when using Baader solar filter?

Generally in the case of noticeable reflections, you should check at first if it is due to light scattered from the edges of the lens. You can try to put a black construction paper with an opening 10 mm less than the diameter of the filter, between the filter and the telescope opening. In photography, this kind of visor can create huge contrast enhancements, especially with camera lenses. In this way (with the additional construction paper in place), you can adapt to a “too large” filter opening without looking hideous and reducing the heat from the telescope. If this doesn’t work, you can try a smaller opening, for example 20 mm smaller than the diameter of the filter.

We hope our suggestions help you achieve the best results in photography. In amateur astronomy there are always some fine tweaking to do by yourself – That’s the beauty of it.

My Baader Solar Filter won’t fit on my telescope even though the aperture corresponds

Detailed question:

Unfortunately the AstroSolar® filter I’ve ordered from you doesn’t fit (just for a bit) on my telescope even though it should have worked perfectly. The clamping isn’t enough for the third bolt to fit. Even though the next filter size fits perfectly, it has a too big opening for me. So if I can’t get the right filter opening, what can I do?


Please look at the filter carefully. If the clamping doesn’t allow for the filter to fit straightly in front of the telescope, we would suggest that you, or gladly us, would slightly file the bolts with a round outwards so that it fits. As a last resort, you could even discard the slots, and simply drill three other holes with 6.5 mm diameter and attach three centering bolts without the slots. There are accessories to close the 6 holes.

The objection to the bigger opening is legitimate. A significantly larger filter opening can cause scattered light from the edges of the telescope lens and unwanted reflections. This would reduce the contrast of the image. It’s best for the telescopes and other lenses that the filter opening is slightly smaller than the diameter of the opening, which lets light in.

However, one should not consider such conditions to be right for every kind of optical systems. For example the primary mirror of a Newtonian reflector telescope is at the lower end of the tube, almost half of the telescopes focal length away from the opening. If someone wants to use the full diameter of the primary mirror with a filter attached at the front, the filter diameter should be 10-15 mm larger than the diameter of the primary mirror, so it doesn’t reduce the light collecting area. This recommendation is more valuable for very short focal length Newtonian systems where the incident light is sharper.

In SC-systems and in other mirror systems with multiple folded light-path, the primary mirror sits less than 1/3 of the focal length away from the main opening and the actual Bernard Schmidt system requires a smaller Schmidt plate diameter than the main mirror. In this case the same diameter as the main mirror is required – that’s why we have these ASTF-filter widths.

How can I find the right Baader solar filter for my telescope?

To make it easy for you to find the right solar filter for your device, we have developed a tool that always finds the fitting filter for your observation instrument. Just click on the image below to open the tool in a new pop-up window.

(You might have to deactivate any ad-blocker for Astrosolar.com in order to use the tool.)

Baader Solar Filter Finder Tool

The Baader Solar Filter helping tool

Can I replace the AstroSolar® film of the Baader Solar Filter in the holder by myself?

Replacement of the AstroSolar® safety film of our Baader Solar filter (for example to put the AstroSolar® photo film OD 3.8) is easily possible. You can read more about that in the manual provided with the product.

When repairing/modifying the product by yourself, you claim all responsibility for the correct application.

Is there a Baader Solar filter with AstroSolar® photo film (ND 3.8)?

Yes, since October 2015, we offer the ASTF- filter with photo film: our Baader Digital Solar Filter. Here you can take a look at the product:

BDSF – Baader Digital Solar Filter (OD 3.8) for High-End Telescopes

Also read: Differences in AstroSolar® Solar Films