Making Your Own Solar Filters for the Upcoming Eclipse

As you prepare for the total solar eclipse crossing America next month, you’ve probably heard a lot about solar filters and safely viewing the Sun. Making your own solar viewers can be an affordable alternative to purchasing premade ones, especially as costs rise and items go out of stock leading up to the total eclipse next month. As long as you have solar filter paper and can attach it properly, you can safely use telescopes, binoculars, and cameras to view the Sun.

Image of the Sun taken through a homemade solar filter using a small telescope. Homemade solar filters are made from exactly the same protective solar filter paper that solar glasses and speciality filters are made from, just attached to devices using a homemade frame. Credit: Rebecca Jean T.

Making your own solar filter is relatively simple. All you technically need is solar filter paper that meets ISO 12312–2 (or 12312–2:2015) standards and some way to properly attach it to your device. The key here is to make sure your solar paper completely covers the surface of what you are looking through. Measure the diameter of the first place sunlight will hit your device. For a camera, this needs to be in front of the lens. For telescopes and binoculars, you similarly need to place the filter in front of the optical tube. A solar filter at the eyepiece may stop some sunlight from reaching your eye, but it will not prevent concentrated sunlight from damaging and overheating your telescope.

Once you know what size solar filter you need, you can just purchase a square the size of your device’s diameter. So a telescope with a 4" diameter will need a 4x4" piece…