Do it yourself -solar filter

When I purchased my new telescope, I also bought a sheet of Baader Astrosolar film for solar observations. I made a cheap and easy solar filter out of Astrosolar film and cardboard. In this post, I will show how to do a similar solar filter by yourself!

For making a solar filter like this you will need:
– 1 sheet of astrosolar film (for example size A4)
– 2 A4 size sheets of cardboard
– glue
– tape
– ruler
– drafting compass
– pencil
– scissors

Phase 1.
First, measure the inner diameter of your telescope. Cut large enough piece of Astrosolar film, it should be at least as big as your scope’s diameter is, but it is convenient to make it somewhat bigger.

Phase 2.
Cut one cardboard sheet in half, then determine the center point of both sheets. Then draw a symmetrical circle (as in picture 1.) around the central point and cut holes in the cardboards along the circle (as in picture 2.).

Phase 3.
Take the other cardboard form and cut it in half. Then put them side by side along their short side. Roll the cardboards into a tube (as in picture 3.) and try it on your scope. The cardboard tube should be tight enough to prevent the filter slipping of in windy weather. After you have tried the tube on your scope, glue the pieces of this tube together. You can use tape to make the seam stronger. Then cut ~1” long and 1,5” wide “winglets” with even spacing in the other end of the tube (as in picture 4.).

Phase 4. Open the winglets and put small drop of glue in the bottom sides of each winglet. Then attach one of the cardboards with hole in this tube with winglets (as in picture 5.). You can make the attachment stronger with tape. Then put this tube on board so that the cardboard with hole is on the top. Then put small amount of glue in it. Take the Astrosolar film, and put it carefully on the glued face of the cardboard (as in picture 6.). Then take the other cardboard with hole and put glue on it and place it on the Astrosolar film. Be very careful in this step to avoid any stains and wrinkles in the Astrosolar film (as in picture 7.)! Then you can tape the edges of the cardboard to make it stronger. And then you are finished!

Now you are ready to start your safe solar observing with your new DIY solar filter (which should look like the one in picture 8.)!

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