Cheap and Effective Filters (solar)





Introduction: Cheap and Effective Filters (solar)

You can buy solar film (thin plastic sheets) at a very reasonable prices online. However, the sheet format isn't great for photography, telescopes or binoculars. You can by them as screw-on filters, but the cost gets a bit ridiculous and the size selection is limited.

This instructable is trivial, but that's where the beauty lies. Using cheap and readily available filter step-up adaptors and UV filters you can fit solar filters to your equipment.

  • Protects film from accidental scratches.
  • Wind protection to stop creases.
  • Holds filter flat and close to lens to stop internal light reflections that can create image artifacts.
  • Looks clean and professional.
  • Made using cheap and readily available parts.
  • Securely holds filters to reduce risk of them slipping and exposing your eyes to magnified UV.
    Important safety feature when using with telescopes or binoculars!
It is important to never scratch or crease the solar film since it might allow dangerous UV light to reach your eyes. If you mistakenly do so while following this instructable, don't try to salvage that section of film, just use a different piece.

This technique can also be used for colored gels!

Step 1: Materials

You'll need a few things you can get pretty cheaply.

  • A cheap, thin "step up ring adaptor".
    Used to attach larger filters to cameras. ($1.20 on ebay)
  • A cheap, thin UV filter. ($3 each on ebay).
    You don't really need the UV protection, you just want physical glass to protect the film.
  • High quality solar film.
    Do NOT go cheap here!!!! 8x8 on Amazon is $18, but it's enough to do a lot of filters. Also, you won't have to worry if you mess up the first attempt.

  • Clean, smooth surface that you can cut on.
    You will be sliding the filter film around on it and you don't want to scratch it. Non-corrugated cardboard, felt, or paper with cardboard under it.
  • Needle
  • Razor
  • Lens cleaning cloth

Again, do not buy solar film from unknown vendors. If you get sold something that isn't really cutting out the UV, then you will damage your eyes and not even realize it until it's too late. It's not as important with digital cameras that use LED screens, but anything involving your eyes and the quality becomes critically important.

Step 2: Step-up Ring Adaptor

What to buy a step-up ring adaptor that is meant to fit slightly larger filters onto your camera.

My camera is 72mm, it says right on the lens.

The step-up ring adaptor is so that I can put 77mm filters onto the camera.

The solar film fits in this buffer between 72mm and 77mm. The UV filter will fit the larger size (77mm) and will hold and protect the solar film in place.

Again, solar film protection is an important feature. If you're using the filter with a telescope or binoculars. You don't want any scratches or folds in the film and the glass UV filter is there to protect the solar film.

Step 3: Trace Solar Film

I experimented with a bunch of ways to cut the solar film and settled on one that works for me. Please suggest alternate ways to cut in the comment.

  1. Place solar film onto a large, thick piece of smooth cardboard or paper or felt cloth.
  2. Place the ring adaptor onto the solar film
  3. Use a needle to trace the outside (77mm) of the filter onto the film.
    Yes, this will be slightly too big

You can see in my second photo that I messed up a little, but that's ok because this circle is bigger than we need.

Step 4: Cut Solar Film

Now that you have a circle traced on the solar film, it's time to cut it.

You'll want to cut slightly inside the circle, but don't worry. There's room for error and if it will probably be too big the first iteration.

4. Place the edge of a sharp razor just inside the etched circle. It should dig into the cardboard under the film and say there.

5. Now move the film and leave the razor in place.
This is a similar action to using a bandsaw.

6. Slide the film around to cut out the circle.

Be careful to not scratch or crease the film.

7. Once you have the circle of film, see if it fit inside the adaptor ring (It probably won't).

8. Repeat the bandsaw technique to shave off a little around the outside until it does fit.

Step 5: Clean and Assemble

Final step is to place the solar film into the ring adaptor and screw on the UV filter.

Naturally, you should gently clean everything of dust first. Just be careful and DON'T use a strong blower on the filter, it will crease it.

Store your final filter in the UV filter case.



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    Great idea.

    Also, consider the Baader solar film.

    Ive used this stuff telescopically, and
    it works very well.

    That site has a scary instructable for using cardboard and tape to "secure" filters onto a pair of binoculars. (PDF)

    Would be nice if they updated it to use the technique I described here.

    BTW, I put this instructable under a public domain license. Sites can either link to it or just create their own white paper based on it.

    Actually, the card board n tape method works pretty well.
    You make a card board cup that
    mates to your instrument with a friction fit.
    Also, since youre looking Up at the sun,
    gravity helps keep the filter on your instrument.
    Ive made 2 of these,
    one for my 3" refractor and
    one for my 8" reflector.
    The baader film works very well.

    Thanks! It's good to have choices since many sellers are perpetually out of stock.

    My filter usage is with OLED viewfinder cameras, but I plan to do one for my telescope and am looking for a better source than Amazon.

    This is one of the best solar films.

    Much better than the Thousand Oaks filter.

    Thanks! I got all the required material (UV filter, up-converter ring, and solar film). HOWEVER, the instructions on Thousand Oaks Optical solar firm I received to build this DIY project indicates that their filter film must be the first element facing the sun, presumably, this means: not obstructed by another filter (such as the UV glass). What are your thoughts regarding that matter? I'm concerned that the glass UV filter element appearing before the solar film, may absorb heat / change the reflective properties of the "mirror like" surface facing the sun. Any thoughts about this?

    What they are emphasizing here, is that the light must go through the filter before it goes through any lenses. Otherwise someone might try putting the filter on the eyepiece end of a telescope, which is extremely dangerous since the sunlight is now concentrated. It's tempting to do this since the eyepiece end is much smaller and therefore cheaper and easier to put a filter on, but DON"T DO IT!

    Ultimately, I did place it in front of the UV filter lens - and actually, it proved to be a very effective construction. I took the idea presented here and did the following:
    - Removed the protective ring of the UV filter. This was a challenge, but ultimately, with four hands and two nails, I was able to unscrew the protective ring undamaged (there are two small slots in which one could put the nails and hold strong while someone else rotates the UV filter).
    - I then cut, with scissors, precisely per the UV glass size, the Thousand Oaks filter. It was very easy an I used cloth while holding the outside portion of the filter polymer.
    - I simply placed lens and then filter, and simply screwed in the protective ring.
    Overall cost for filter was exactly same as in description, but the first element to the sun was the filter, as required.
    Ah, one can remove the need for the step-up in this way - the whole lens is well covered by the filter.
    Worked very well for 2017's total eclipse - now, just in wait for 2024 ...