Intro: Solar Filters for Binoculars
On Aug 21, 2017 a total solar eclipse will be visible coast to coast in the United States. The diagram above is from http://eclipse.gsfc.nasa.gov Millions of people will be able to see it as it sweeps from Oregon to South Carolina. Before and after the total solar eclipse there will be partial phases. The sun will be too bright to view without proper equipment. One should never look directly at the Sun. Your vision is AT RISK! This instructable is about making a safe set of binocular filters. The MOST important purchase is to buy safe filter material. I brought a letter paper sized piece of Baade solar filter film for about $20. You can find several suppliers on the Web but I would recommend buying from one of the large amateur telescope companies that have long experience in selling the film and not taking any risks with your vision for a dollar or two. .
Step 1: A True Story
I saw my first solar eclipse while I was in high school a long time ago. In that distant past even the telescope companies sometimes provided rear solar filters that fit the eyepiece of a telescope. There were articles about making jury rig filters using smoked glass and exposed 35mm film. Looking at the Sun through a jury rigged filter is dangerous. My filter melted in the heat and I was lucky that my friend was standing by and noticed. I was lucky I didn't look through the telescope and to not to have my vision damaged. DON'T do what I did.
Step 2: Choosing Binoculars and Filter Holder Template
The first step is to choose the size of binoculars you are going to use. The Sun happens to appear about the same size in the sky as the Moon. I would suggest looking at the Moon to get an idea of how large the Sun will appear. My binoculars are 15x60mm. Measure the outside diameter of the front of the binoculars. Mine were about 72mm. I then made a cardstock template with 72mm circles. Use both circles to make the front and back of the filter holder.
Step 3: Cutting the Template
Next cut one side out entirely and the other cut into triangular slices. For the triangular cuts Cut to a little beyond the circle so when we fold the flaps back the cutout will include the entire circle.
Step 4: Fold Back the Flaps in the Rear Filter Holder
Step 5: Cut the Solar Film
I needed a piece of film 80 mm square to cover the circle completely. The film is easily cut with scissors. I made a score with a razor knife to mark where to cut the film.
Step 6: Tape the Film to the Front Filter
I taped the four corners of the film being careful not to have any wrinkles. Put some glue carefully around the edges, align with the other half of the filter and seal in the film.
Step 7: Finished Filter- Front and Back
Here is a front and back view of the finished filter holder. I mounted the filter to the front of the binoculars with a wide rubber band. For extra security I think bending the flaps over the rubber band and taping everything in place is a good idea. Remember your vision is at RISK. Be careful if it is windy or with children present. IIMPORTANT do not use a filter like this at the rear of the binoculars. The heat buildup from the concentrated sunlight could damage the film and your eyes.
Step 8: Filters Mounted and Links
Here is the filter mounted on my binoculars. Obviously making a second one is just like the first. Or you could just cap the other lens and use as a monocular. I also bought a bracket for holding my binoculars on a tripod. The partial phases will last hours and holding them without damaging the filters would be a chore. The filters I have produced an orange colored Sun and I clearly saw a nice sunspot group today (June 19, 2016). Useful link for finding SAFE solar film and solar viewing glasses and where to see the eclipse. http://www.greatamericaneclipse.com