Instructables

Floppy Disk Sun Filter

Picture of Floppy Disk Sun Filter
Several months ago I posted an Instructable about making a simple sun filter with a black marker and a sheet protector. That approach, although it did block out most of the light, didn't work very well and threw everything out of focus. This one, using a floppy disk and some card stock, works much better and doesn't take anywhere near as long to make. There's also slightly less of a pink color, though part of the blue component of the color seems to be from UV that makes it through the filter. The effect seems to go away when used with a telescope for some reason. Instead, the disk filters the light to a more realistic orange.
 
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Step 1: Supplies

Picture of Supplies
You'll need a camera with optical zoom (this is important, you'll be using the lens barrel to keep the filter attached) a floppy disk, some thick paper, glue, scissors, and tape might be helpful in assembling the mount.
I'm also using an old computer as a surface. You can use any old computer you  might have laying around, or you can just use a normal table.

Step 2: Open the disk

Picture of Open the disk
This is probably one of the harder steps. You'll need to rip open the disk, but be careful not to crease the black magnetic film because we'll be using that. Pop out the metal wheel and throw everything away except the film. You could also reuse the parts for something else, but recycling is not the goal of this ible.

Somehow this photo ended up upside-down even though it looks fine in Photoshop.

Step 3: Cut the disk and put the filter together

Picture of Cut the disk and put the filter together
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Cut the magnetic film into 4 pieces. Layer two of them on top of one another, and glue or staple them together at the narrow end and on one side. This will allow you to add or remove layers without having to tear apart the filter and rebuild it every time you want to change how dark the image should be. I also recommend opening another disk and cutting that one into 4 pieces if you want to use the camera with a telescope.

Trim the extra pieces so they have tabs on either of the sides you left open on the "pocket". Again, this is so you can add and remove layers without destroying the filter or switching to a lighter or darker one. Put them into the pocket. You're done with the filter, but it needs to be attached to the camera somehow, and the rubber band/staple trick won't work for this camera.

Step 4: The mount

Picture of The mount
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Cut a piece of paper that's more than big enough to go around your camera's lens barrel. I had to have my camera turned on to do this, so be prepared to use up some battery power. Charge it or replace the battery if it's dead before making the mount.

Wrap it snugly around the barrel, and tape it in place. Next is the tricky part. Try to trim the tube to no longer than 1/4" beyond the lens. The filter needs to be as close as possible to the lens to get the same FOV as you get without the filter.  Once it's trimmed and taped together, take it off of the camera and glue it to the filter. Let it dry.

Step 5: Finished

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Once it's dry, go outside with the filter on the camera and take a few pictures of the sun. Put in more filter layers if it's too bright to see the photosphere without any glare, or take some out if you can't see anything. If you're planning on using this with a telescope, don't use a very high magnification and make sure that there's enough cloud cover to act as a filter, or else the filter will melt and all that work will be ruined. Possibly your camera, too.

And if your camera has a viewfinder, DO NOT USE IT WHILE LOOKING AT THE SUN. Unless you've made a second filter just for the viewfinder, even then it's still dangerous. It's best to put some electrical tape over the viewfinder or something.
georgeATM2 years ago
Please note that using homemade filters should only be used for photography and not visual observing. Solar observing is the only activity in astronomy that is inherently dangerous. Using any filter that is not specifically designed for this activity can be dangerous because there are wavelengths of light that the human eye can't see but are still harmful to the structures of the eye, specifically ultraviolet and infrared, that may be getting through the filter. Galileo's blindness in old age may have been caused by observing the sun.

End of scary rant.
Kudos on a fine instructable.
tbh-1138 (author)  georgeATM2 years ago
I included a warning on the last step. I have no idea what wavelengths can get through 4 or 5 layers of floppy disk material, other than that it only lets red and orange through. I'm sure plenty of IR passes right through, as I've seen another instructable using a floppy disk as a filter for IR photography. It would be nice if there were a way to make a filter that first blocks everything but the UV, then shift the UV into the visible range. From what I've seen in SOHO and STEREO photos the sun looks awesome in UV.
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