Elad Orbach : schlieren on a stick

Schlieren imaging

Wikipedia: https://en.wikipedia.org/wiki/Schlieren_imaging

MIT: http://www.mit.edu/~milesdai/projects/schlieren/index.html

NASA: https://www.grc.nasa.gov/www/k-12/airplane/tunvschlrn.html

Schlieren photography is similar to shadowgraph imaging. Both are optical methods that reveal nonuniformities in transparent materials such as air, water and glass.

Schlieren imaging relies on the fact that light rays bend whenever they pass through changes in refractive index. In air, these changes can be caused by differences in temperature, pressure or density.

Shadowgraph example showing a bullet in flight:

https://en.wikipedia.org/wiki/Shadowgraph

How it works:

http://www.ian.org/Schlieren/HowTo.html

What you need

A spherical, parabolic or concave mirror

A selfie stick long enough to reach approximately twice the focal length of the mirror

A cellphone using its camera and flashlight together

The mirror does not have to be large, but a larger mirror provides a larger viewing area. For this portable version, I was looking for the largest, lightest and cheapest mirror I could find. I also considered using an acrylic mirror to reduce the weight.

A spherical mirror should provide more uniform results with this setup.

How to adjust it

Attach the mirror to the far end of the selfie stick.

Mount the phone near the selfie stick handle with its camera and flashlight facing the mirror.

Extend the selfie stick until the reflected image of the flashlight becomes as small as possible. This should happen at approximately twice the focal length of the mirror.

Adjust the phone until the reflected flashlight covers the camera lens.

Zoom in, adjust the contrast and enjoy your new toy :-)

Photos of the intended selfie stick setup are below.

Video:

https://www.youtube.com/watch?v=Oc6QV4PmXDk

Some more videos:

https://www.youtube.com/watch?v=nTyBUgBCJBo

https://www.youtube.com/watch?v=RoTymzMcHj0

Some notes

The selfie stick was too flexible to produce stable results. I need to find a stronger selfie stick or replace it with a carbon fiber tube and make another video.

The automatic exposure of the cellphone camera drove me nuts. I need to find a proper video application that allows the exposure and focus to be locked.