Schlieren Flow Visualization is a method to see small differences in air pressure like those around a flame; essentially it allows you to *see* air. It is typically accomplished with super fancy mirrors that can cost upwards of $300. This instructable is about making a Schlieren Flow Visualization really cheaply and pretty easily. If you are curious about my failed attempts before I got it to work then visit my DIR Schlieren Flow page.
Here are all the components you need:
*other cameras might work too but I couldn't get the effect to work with my point & shoots.
The basic idea is you need to get something hot like a candle in the middle of some parallel light rays - then focus those rays back to almost a point – knocking out half of the rays that didn't line up exactly parallel. The first page magnifier makes the light from the LED parallel (collaminated) then the other one focuses the light back again. The camera is placed right where the light focuses and angled to the side so that some non-parallel rays are blocked by the aperture.
You need to position the camera carefully, but patience is an ample substitute for fancy equipment :O
All the elements need to be lined up in a row, using a nice long table will make access comfortable, but you could also use any hard floor.
Folding the cardboard into triangles and cutting a slit for the magnifiers was sufficient for holding them up straight, it doesn't need to be that perfect. The LED should point straight towards the magnifier, I taped it in place. With the LED on, moving a piece of paper back and forth in front of the magnifier will help you find when it is parallel (it won't expand or contract).
The camera should be held up so that lens just touches the point that the light rays focus. You could use a tripod, or just some books and a stool or chair like I did at first.
The trickiest part is focusing the rays. If you are off by a lot then you won't get any hint of the right direction to move the camera in. If you get close enough to see something though – move the camera to maximize the area of the screen covered while maintaining the camera at about a 45 degree angle. This above video shows what it looks like as the camera is moved around. It can look a little different depending on which direction the magnifiers are facing (they are not symmetrical) but the effect is still there no matter which way they face.