Making of Solar Filter from Baader AstroSolar Film

In my previous post, I mentioned my reasons for ordering the Baader AstroSolar film in preparation for photographing the transit of Venus. In this post, I will describe the process that I adopted for making a solar filter. The filter can be fitted to any D-SLR lens using a standard Z-PRO Cokin ND filter holder. My design choice was primarily dictated by the fact that I will be using my D-SLR with a telephoto zoom lens (most likely my Canon EF 70-300mm f/4.5-5.6 IS USM) instead of a telescope, and I already have the Z-PRO filter holder. The Baader film came with instructions on how to construct a Filter Cell for using any telescope; you could also follow their instructions to construct your own filter. I don’t think, from an image quality standpoint, that there is any fundamental difference between the two ways of mounting the filter in front of your lens. Their recommended way is suitable if you are using a telescope, or you don’t have a filter holder like one mentioned here.

The picture below shows all the material that you may need (I actually ended up using a blade too and didn’t use the gloves at all) to construct the filter. I was extra careful not to touch any part of the film with my figures. Things to note in the picture are two 4×6 size photo mat that I bought from Michaels, the AstroSolar film (unrolled slightly), and the Z-PRO Cokin filter holder on the top right.

The basic idea is to sandwich a piece of the AstroSolar film between two (appropriately sized) photo mat. As pictures are worth thousand words, I will mostly let the pictures speak for each step. 

Raw material

Raw material

Step 1: As the mats were just a little too big to fit into the holder slots, they were first cut into the appropriate size.

Sizing the mat

Sizing the mat

Step 2: The two flaps that will be used to sandwich the film between them are shown below, which were cut into the appropriate sizes.

Top and bottom of the stack ready

Top and bottom of the stack ready.

Step 3: Applying synthetic adhesive to one of the flaps.

applying adhesive

Applying synthetic adhesive (fevicol) on the bottom side of the top flap.

Step 4: Carefully place the flap, with adhesive on its bottom surface, on the AstroSolar film. The AstroSolar film does not need to be “stretched”. In fact, Baader recommends that it is more desirable to have slight wrinkles than to stretch the material as stretching will damage the optical quality and the coatings. “Wrinkles, creases and folds in the material are normal and will not affect the function and performance in any way” [quoted from “Making an Inexpensive Filter Cell for BAADER AstroSolar(TM) Material”] (I am not completely sure about the accuracy of their claims, as I believe that parallel light rays incident on the surfaces which are at slightly random angles due to wrinkles, will not emerge parallel. However, without having done any experiments of my own, I will assume that their claims are true since the film is a very thin foil of about 0.012mm.)

flap on astrosolar film

Carefully placing the top flap on the AstroSolar film.

Step 5: Cut out the frame with the film stuck to it from the rest of the AstroSolar film.

separate out the frame

Cutting out the frame from the rest of the AstroSolar film.

Step 6: Before sticking the bottom flap, a quick and dirty test was done to check for any pinholes or extreme scratches, that could potentially cause light leakage and loss in contrast, by placing the filter against a bright lamp. You can see the filament ring towards the center-left within the AstroSolar film area.

quick test

A quick and dirty test to check for any pinholes, scratches, etc.

Step 7: Once I was sure that there weren’t any pinholes or scratches, the lower flap was glued to the rest of the sandwich to complete the filter.

adhesive applied to bottom flap

Synthetic adhesive applied to top surface of the bottom flap.

Step 8: The filter was then carefully placed under the weight of two books on either sides and kept for a while till the adhesive dried.

The AstroSolar film sandwiched between the two flaps. Two books placed on the sides as weights while the adhesive dries up.

Once the filter was ready, it was time for a quick test. The two photographs below show the completed solar filter fitted to the camera’s lens using a Cokin Z-PRO filter holder.

The completed filter fitted to my Canon 70-300mm lens using a Cokin Z-PRO filter holder.

Side view of the solar filter with the camera and lens.

With the lens zoomed to 300mm, I took a hand-held photo of the afternoon Sun. The picture below shows the area that the image of the Sun occupies within the 22.4 mm x 14.8 mm  frame (Canon APS-C sensor). [More on image size of the Sun with respect to the focal length and sensor size will be a topic for another blog post.]

A hand-held (test) photograph of the Sun.

The picture below is a cropped and digitally (zoomed-in) version of the above image. The diameter of the Sun’s image is 417 pixels across, which is approximately 2.67 mm (assuming square pixels) since the pixel pitch for the sensor is 6.4 microns. Although the photograph is not tack sharp (possibly because it was hand-held telephoto shot), one can still see the solar spots on the surface. No, they are not sensor dust, I have double checked that. (Please bear in mind that I wasn’t trying to get the sharpest possible photograph of the Sun in this experiment.)

Solar photograph zoomed-in

Cropped and zoomed version of the first (hand-held) photograph of the Sun with the Baader AstroSolar filter. The diameter of the solar disk in this image is 417pixels (= 2.67mm)

I think I am pretty happy with what I have here in terms of the solar filter. I will be doing more experiments with it and will write about it soon.  Please stay tuned for more.



  1. Kool, I wish I had seen this before the material was sold out!

    1. Hello Anangelu,
      If you are in the US, you can still order the 3.8 Density “photographic” (NOT FOR VISUAL!!) version of the Baader AstroSolar filter from ASTRO-PHYSICS. Link: (I just saw that the 5.0 Density visual filters are sold out, but they still seem to have the photographic ones). Also, note that even if you don’t find the Baader films (I am not recommending this, and please use it with extreme caution), you could get Mylar films. They are also known as “Emergency Thermal Blankets” (from Amazon for example). If you use the thermal blanket, please use TWO layers of the sheet to construct your filter. In the past, I have used a double-layered thermal blanket to photograph solar eclipse. You may see the results here:

      1. Marvelous, I ordered from Amazon and of course today was like THE deadline. I will have filter case already designed and ready to stick in the ” Emergency Thermal Blankets” following your advise. I hope I can get a good picture at least. I wouldn’t have known by that name what it was. Thank you!

      2. Great! I am happy that you have ordered the Mylar thermal sheets to make your filters and I am sure you will get some great photographs. You are most welcome to post a few of your Venus transit photographs in this blog if you like. Also, check out the following posts if you have not already (I think they are useful):
        1. Recommendations on photographing the transit of Venus
        2. How big will Venus be in my camera?

        Also, if you think that it will be very windy at the place where you will be photographing the transit of Venus, I will strongly recommend that you adapt a filter development method described by Tim Cole here.
        Good Luck.

  2. Scott · · Reply

    I ordered some film tonight I am unsure if I will get it prior to the deadline but I hope so. I also ordered a H-Alpha filter! Is this able to be used with the solar film (I presume yes)

    1. Hi Scott,
      I am not really an expert in this area, and I don’t have a H-alpha filter to try it out. But this is what I feel – The Baader AstroSolar (photographic) film reflects back 99.984% of the light (including Hydrogen alpha band) letting through only a very tiny fraction of the incident light into the optical device (camera or telescope). It is also placed in front of the (objective) lens. When the H-alpha filter is placed behind the AstroSolar film, it receives only 0.016% of the light which is further reduced when this light passes through the H-alpha filter. So, in my opinion, the H-Alpha filter may not work (at least as intended) when combined with a AstroSolar film.
      Normally an Energy Rejection Filter (ERF) is used in front of the objective lens (as opposed to an AstroSolar film) when coupled with a H-alpha filter. As an example, see the C-ERF filter from Baader -

      That being said, I would encourage you to experiment with the Baader AstroSolar film + H-alpha filter combination. It would be great if you could post the results for all us to see and learn (if that is fine with you).
      Thank you very much.


      1. Hopefully it all arrives in time, I am thinking the film will get here first as its in Aus and the filter is coming from the States. I only just realised that the H-Alpha filter I have purchased is a sky one and not full solar, I realise this will limit the amount of detail that I get. This will be my first attempt at Solar photography. I will be using my Nikon D800 with my 80 – 400mm VR on Manfrotto tripod. I am currently researching telescopes and connectors as I type this.

        I have no issues posting photos and would like any feedback thats available.

      2. That’s great! Good luck with your pursuits.

  3. since I will be making my filter with two sheets of the mylar material, I would like to ask, how safe it is to look through the camera with this? Do I need to buy a pair of special glasses? I don’t think I can find them on any store now.

    1. Well, technically a double layered mylar thermal blanket reduces the intensity of light much more than a single layer of AstroSolar film. See this blog post. It is reflective type, unlike the common photographic ND filters which either absorbs energy in certain wavelength or just lets through, and so, the mylar filter reflects back most of the light (including light in the UV and IR region). Also,I have used double layered mylar sheets in the past to do solar photography (including looking through the viewfinder). However, I will NOT ADVICE anyone to do so because I don’t really know if it can cause damage to the eyes [there are no studies] if used for a prolonged amount of time, which I think will be the case during the transit of Venus. If you can attach your camera to a laptop and focus using the view in computer, that would be perfect! For example, all Canon DSLR cameras can be easily attached (using the USB cable) and controlled using the Canon EOS Utility. (It just occurred to me that I should actually try out this method too, to see how useful it can be (probably I will try it out today)). In summary, my recommendation will be try to avoid looking through the view finder as much as possible if you aren’t using a computer.

      1. Anangelu · ·

        I think I will use the canon s/w with a very handy small Asus PC for the first time, o I have to practice this. My eyes are priceless. Thanks!

      2. That’s just perfect!! Right now, I wish I had a small laptop (I have a powerful, but huge, Sony Vaio 17″ laptop). Using the Canon software is pretty easy, but I will recommend that you try the combination ASAP to make sure it works. I am telling this because, you could run into some software compatibility issues and should resolve it as soon as possible. For example, the older Canon Utility that came with my Canon Rebel XT and 5D (1st generation) doesn’t work on Windows 7 and so I use windows XP (virtual) to connect and control my older cameras. I am 100% in agreement that our eyes are priceless.

  4. Reblogged this on Indranil's world and commented:

    Re-blogging my own post from the blog dedicated to “The Transit of Venus 2012″

  5. Just fr other to know, the Canon software does not run under 1024 x 768, the Asus is 1024 x 600. Any other program that I can run at that resolution? The hardware doe snot go higher than this.

    1. Oops! That’s news to me. That’s so dumb from Canon! If you have a newer DSLR and if you have (I think) version 3 or above of Adobe Lightroom, you may be able to control the camera using Lightroom (I have never tried it though, so I am not sure).
      As a last options, I would do the following — use a double layered mylar sheet in front of the lens, and for extra protection (if needed) I would just cut a small strip of old photographic film negative and fix it to the viewfinder’s cap. I know it is a little clumsy, but it works!

  6. I will definitely use the film on the viewfinder….

    I do have Lightroom but on my Mac which is a desktop… . The Asus is small and Windows 7. Anyway I partially solved the problem with $20. I bought DSLR Camera Remote (an App) and ran its free version. It tested well. Bought the $20 App and tested it. I can shoot as many photos as I wish from my phone controlling aperture, size and several other things. It even can send the photos to a hard disk of a computer to which you have to attach the camera, without looking, but I cannot see the image before taking the photo. At least I have to look once to focus, but in this case, focus is infinity so there should not be any problem.

  7. Thank you so much for the follow up ideas. I will test everything tomorrow as I have it now when the mylar arrives which I hope it does early.

    The app is great. It can even do timelapse, burst and control a few other parameters.

    1. Good to know that you have found a solution you like. By the way, does your camera have a live-view? (I know it might be a silly question, because if it did then we wouldn’t have had all these conversations … still, I was just checking).

      1. It has, so maybe I don’t know what it is for ;-( I know I can use it to see a live preview of the viewfinder, but it doesnt happen like that with this App setting. I don’t know why. The camera is a T2i

  8. I have to apologize, and I have to go back and mend the review I gave to this App.It was so simple to solve! I had to enable Live View at the App ( iPhone) in order to see what the viewfinder shows. Dah! I feel so dumb! Anyway, I am now almost complete and ready. It was a $20 bill well spent on the App.

    1. I am happy that everything is in place now and you don’t need to risk your eyes. I was just about to send you a link ( that describes how you could focus in the live-mode (through your LCD) in the T2i. So, technically, you don’t even need the app! However, I guess, the app is pretty cool anyways and well worth $20. Good luck, and it would be great if you could post some of your photographs here (no obligations of course). Thank you.

      1. Anangelu · ·

        Posting photos: Only if they are good and that doesn’t happen too often. I love showing my work, but, I had ever imaged the sun. I will have family staying over WITH KIDS that day, touching down at airport at 1:00pm, what a luck! It’s just an overnight in transit for their cruise. Will this be too much with 2 kids around? I guess they don’t even know what is going on in the sky that day. I know live view would allow me to look at what is going on thru the lens, but since the camera is usually looking up, I would have to be kneeling below the camera a really difficult position for my back and legs. T2i Does not have an additional swiveling screen and that is when the App come more than handy. I usually use an external monitor, but it is cumbersome, adding more cable and a 7″ monitor that needs some kind of a stand or table. The App can serve as an intervalometer, to make time lapses, I can change aperture and other from the iPhone. It’s a gem!

  9. Anangelu · · Reply

    Ready to go! Btw, I hope the kids do not stand on the way and let me image this marvelous event. It could be a very nice learning experience for them, but being preteens, I doubt they will stay put and NOT look at the sun OR be in the way.

    Only piece required, Mylar, is not yet in, but it is only 9:00AM!

    1. Posting photos: I completely understand, and I guess I would do the same 🙂
      I am sure it will be an interesting day, so have fun. May be the kids can get a lesson or two about the Solar System. (That was really me, trying to be optimistic, I would really not want any disturbance during that time!) Kids can be pretty tough to manage, as it might be very difficult to make them understand why they shouldn’t be looking at the Sun directly or things like that. I guess your iphone app could be very useful tool here. On that note, I would just like to mention that, the first 18 minutes are the most important (assuming you are in the US).
      Regarding the looking up issue: I agree it can be quite painful to bend one’s body in strange ways to look through the viewfinder/LCD screen of a camera pointing upwards. I actually have a pretty tall tripod and I keep the camera a little above my eye-level. It is not that uncomfortable for me.
      The app: It seems like a good one. Now, that you have intervalometer (among other capabilities of the app), your photographic possibilities have increased.
      Hope you get your Mylar sheets come pretty soon.
      [OK, for once, I just want to make sure that you have ordered the right kind. I am a little concerned because you always mention “mylar sheets”. I understand that this could just be because you are typing on the iphone…But “mylar sheets” are (plastic) sheets of Mylar material. The “Mylar thermal blankets” are made my depositing layer of aluminium on Mylar sheets. They look like mirror surfaces, and are useful for DIY astrophotography projects such as this. I am sorry for bringing this up … but I wanted to be sure, as using the wrong material can cause damage to the camera and/or your eyes. Also, note that there has been “edits” :-)]

      1. Don’t be sorry about making something clear. You could be surprised of what people can understand of one says. It happens all the time.

        I understand the concern, my friend… I ordered the right stuff at Amazon: Mylar thermal blankets. But, the “sheet” comes into play because I will have to cut a piece to fit the holding frame and then… it will be just a “sheet” of the Mylar material, not a “blanket”. Sooo, it’s a manner of speaking, but it was worth clarifying so no one could misinterpret what we are talking about.

        I also have an physical intervalometer, but the bending situation (I am 65) made viewing a problem, until I acquired the monitor, which has served me very well. Now, I am glad I don’t have to hook up the monitor, but I have to tether the camera to a PC running a server program (free, downloadable). The good thing about the App is that it sends the photos to the hard drive, so you streamline the process by having the photos already saved when you finish your session.
        Anyway … there is always something to hook up on my three scenarios: 1) intervalometer (no view) 2) PC + App and … 3) 7″ monitor attached to camera.

        As you see we need to keep adding and adding things for special purposes until we go out and have to carry a bunch of equipment for a night of astrophotography. That is how it is!

        Well, good day and clear skies!

  10. I just followed your guide and made a filter for the transit of Mercury! While the clouds did not cooperate, I’m ready for the next chance in three years.

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