EDIT: I no longer recommend this method because I've found a much, much better way to make a sun filter.
https://www.instructables.com/id/Floppy-Disk-Sun-Filter/

Ever wanted to take a picture of the sun but can't afford a solar telescope? Here's how to do it with a sheet protector and a Sharpie.

Materials:
Sheet protector
2 rubber bands
Any permanent black marker
Stapler
Scissors

Step 1: Cut

Cut the sheet protector along the right side and the bottom. When you're done it should open up like a book. Cut one of the two "pages" off. Unless you want an extra-strength sun filter or you want to make two, throw the other half away. Take the piece you cut off and cut it into 8 pieces.

Step 2: Color and Assemble

On six of the eight pieces, draw a huge black blob on both sides with the marker. On the two left, draw a huge black blob on only one side. Stack the six double-sided layers on top of one another. Put one of the single-sided pieces on top of the stack, ink side down. Flip the stack and do the same with the other single-sided piece. Staple the stack together at the corners. Now staple the rubber bands on either side of the blob. These will hold the filter on the camera.

Step 3: Shoot!

Put the filter on the camera, with the black blob over the lens. Go outside and take a few pictures of the sun with the camera. The pictures will be tinted magenta by the not-so-perfect black ink from the marker, but other than that the pictures look great! If you don't mind melting the filter a little, try aiming a telescope at the sun and use your filtered camera to take pictures through the eyepiece. Do NOT use the viewfinder if your camera has one. Cover it with black electrical tape or anything else opaque. If you absolutely must use a viewfinder (if your camera doesn't have a screen) make another, smaller filter and attach it to the viewfinder.