Introduction: Solar Filter for Smartphone

All amateur astronomers like myself out there started out pretty much the same way. We usually get our first telescope or binoculars and start out observing the moon, then quickly move on to the planets, and then the deep sky objects. But in all of that squinting into my eyepieces, trying to see fainter and deeper stars, I completely ignored OUR star. The Sun, that giant, nuclear reacting, Hydrogen gas burning, ball of light right above my head!

I don't have to squint to see it, it's so bright I can't even look at it. And yet I never thought, if I want to know about stars, why not study the closest one to me? Now to answer that question. Scientists say the Sun is 93 million miles away, yet it will blind you if you look at it with the naked eye. Also, you will get burns from the Ultraviolet light coming from it if you stand in the sun light for more than a few minutes unprotected. It actually is scary if you think about it for too long.

The Sun is considered a yellow dwarf star, and it is believed to be traveling through space at a speed of over 330 earth miles every second, dragging us along with it. It may seem everything in space is fixed in one place, but because of the great distances between things you just cannot see the movement that is happening.

Anyway, observing the Sun is DANGEROUS if it is not done correctly. I am going to show you a simple lens for a smartphone you can make at home for observing the Sun and recording what you see. NEVER view the Sun through anything that does not have a filter in front of the lens. Usually, viewing the sun through a digital device is safer because you will be looking at the sun on the devices screen, which can not get bright enough to blind you, but is still way to bright to focus on. This filter will correct that, and allow you to photograph the sun. It will work great for eclipses, but if you want to look at sun spots, or transits of Mercury or Venus, you will need a special telescope, or a filter for a regular telescope.

Still, I must make the disclaimer that I am not responsible for any injury, damage or loss associated with making or using this filter. Always keep safety and good common sense with you when observing the Sun, and never cut corners.

Step 1: Tools and Materials

I will give you the list of things I used to make this filter with, and the tools I used, but these are not the only things that will work by far. I usually make things out of whatever junk I have lying around (which is all my barn / workshop has in it) when I set out to make things. A good rule of thumb for makers is nearly everything can be used for something, even if you can't think of what it could be at the moment, so I save everything we "through out".

We are going to be making a smart phone camera filter. I do not recommend making homemade filters for binoculars or telescopes without getting the proper type of filter, specifically made for this job. Homemade filter material is just not worth the risk of using on these things. One look into binoculars or a telescope without the right filter WILL BLIND YOU!

That is why I like digital devices. You can filter the light going into the camera, and safely view it through the devices screen. Now one more word of caution. I have used this filter for short periods of time with no effect on my phone, but I cannot rule out the possibility of damage to the device or its camera. My phone is old,( old for electronics anyway, an IPhone 4) so I experimented with it without danger of major loss should it have gotten damaged. But so far it is good.


Ball-Peen hammer

utility scissors

regular scissors

box cutter

wet erase marker



super glue


old cd or dvd discs

metal brackets used for mounting window blinds

weather stripping

electrical tape

spray paint (optional)

Step 2: The Frame

1; The bracket I used was in the shape of a U, which is the shape you will need, but it will need to be more narrow to fit snuggly around your phone. To accomplish this you will need to straighten one side of it and then bend it again back into a U to match the thickness of your phone.

You will notice in the photo that one side of the bracket has a oblong hole in it. You want to leave this side alone. Since all phones are different sizes, this oval hole will accommodate for the differing distances of the camera lens from the edge of the phone for most types of phones.

Next flatten the back of your bracket. You may have to start this with pliers, then move on to the vise or use a ball-peen hammer on it until this part is completely flat. Again leave the end with the oblong hole at it's 90 degree angle, this will be the part that goes over your phones camera, and it will look better if it is not reshaped.

Measure how thick your smart phone is, then find something hard that is slightly thicker than your phone. My phone, an IPhone 4 is around 5/16 inch thick. I have a wrench 1/2 inch thick, so I bent the bracket back into it's original shape. It fits much more closely around my phone, but still does not touch the phone.

If you would like your frame to be a specific color, cover the inside surfaces with tape, then spray paint the frame whatever color you like. Not painting the inside will help the glue we will use later stick better.

Step 3: CDs for Filters

cd's look solid but are actually see through in some places, where both the front and back are shiny silver. Hold a cd between you and a bright light bulb. In the silver areas you will be able to see the bulbs filament glowing, but almost no light. these are the areas of the cd we need to filter sunlight. Cut out these areas with utility scissors, but watch out, it will be sharp on the cut edges. Try to get CDs or DVDs that don't have a lot of scratches, as these will effect your photo quality.

You can split a CD into its two halves by inserting a box cutter into the edge and giving it a twist, but it is more risk of cutting yourself, and it is not necessary. You will need two pieces of CD to filter out enough sunlight to be useful. Cut both pieces so they are the same size and shape as the inside part of the bracket with the oval hole in it.

Glue these together around the edges with super glue. Liquid super glue, if it is not used in very small amounts will spread across the filter between each piece through what is called the Capillary Effect, so go easy on the glue to hold the filter together.

Once they are dry, glue the filter inside the frame, making sure it covers the entire oval hole so no light leaks through. If it needs to be sealed, a few pieces of black electricians tape placed around the inside of the hole, but not visible from the outside should create a good seal.

Step 4: Padding

Next, cut away the thin edge of the weather stripping for padding. This will take up enough space inside the frame that it will fit tightly over the phone through tension, and will keep it from scratching the phone. Cut pieces to fit neatly on the remaining inside surfaces of the frame. Do not cover any part of the filter with this, the closer the cameras lens is to the filter the clearer your image will be.

My phone and both pieces of filter glued together came out to 7/16 inch thick, so that left 1/16 inch of unused space, just enough for the weather stripping to create a good hold on my phone.

Finally, if there are any edges you are worried about with your phone, cover them with a small piece of electricians tape. I had only one.

Step 5: Done!

Your filter is ready for use when all glue has dried. In the photos you will see one that is way too bright. This was an attempt using just one piece of CD. It toned down the brightness a lot, but not enough. The second was taken using the completed filter with both pieces of CD. You can get a perfectly clear shot of the sun's disc. Again, this will work great to document a solar eclipse through photos taken every few minutes, or if you can do it with your phone, live stream a video of the eclipse, or record it for a time lapse video.

Again, please be safe. Hope you enjoy this!

Explore Science Contest 2017

Participated in the
Explore Science Contest 2017