Schlieren photography is similar to the shadowgraph (an optical method
that reveals non-uniformities in transparent media like air, water, or glass)
and relies on the the fact that light rays are bent whenever they encounter changes
shadowgraph (bullet in flight - wiki)
what you need
*spherical / parabolic / concave mirror (the biggest, lightest,
cheapest you can get) acrylic?
rigid selfie stick (length depends on the mirror focal length)
cellphone (video mode with led powered on)
*spherical mirror will achieve better uniform results
how to adjust
glue the mirror to the far end of the selfie stick
hang the phone on the selfie stick handle
extract the selfie stick to the point which the reflection of the led
seems to be smallest (about twice the focal length of the mirror)
and that the led reflection covers the phone camera lens
zoom in, adjust the contrast and enjoy your new toy :-)
photo of the wanted (selfie stick) setup
some more videos
need to find a robust selfie stick (carbon fiber?) and make another video
auto exposure of the cellphone app drive me nuts need to find
proper video app with fixed exposure
photo of the wanted (selfie stick) setup
and a video
some more videos
some notes
selfie stick was too flexible to get solid resultsneed to find a robust selfie stick (carbon fiber?) and make another video
auto exposure of the cellphone app drive me nuts need to find
proper video app with fixed exposure
further reading:
Raffel, M. & Heineck, James & Schairer, Edward & Leopold, Friedrich & Kindler, Kolja. (2012). Background Oriented Schlieren techniques for helicopter related large scale and flight testing. 38th European Rotorcraft Forum 2012, ERF 2012. 2. 1-9.
https://epjtechniquesandinstrumentation.springeropen.com/articles/10.1140/epjti/s40485-018-0045-1
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