A magnifying glass is seen behind a small tea candle. The magnifying image is projecting the shadow of a column of heated air.

Finding Simpler Schlieren Imaging Systems

October 6, 2025 by Aaron Beckendorf 3 Comments

Perhaps the most surprising thing about shadowgraphs is how simple they are: you simply take a point source of light, pass the light through a the volume of air to be imaged, and record the pattern projected on a screen; as light passes through the transition between areas with different refractive indices, it gets bent in a different direction, creating shadows on the viewing screen. [Degree of Freedom] started with these simple shadowgraphs, moved on to the more advanced schlieren photography, and eventually came up with a technique sensitive enough to register the body heat from his hand.

The most basic component in a shadowgraph is a point light source, such as the sun, which in experiments was enough to project the image of an escaping stream of butane onto a sheet of white paper. Better point sources make the imaging work over a wider range of distances from the source and projection screen, and a magnifying lens makes the image brighter and sharper, but smaller. To move from shadowgraphy to schlieren imaging, [Degree of Freedom] positioned a razor blade in the focal plane of the magnifying lens, so that it cut off light refracted by air disturbances, making their shadows darker. Interestingly, if the light source is small and point-like enough, adding the razor blade makes almost no difference in contrast.

With this basic setup under his belt, [Degree of Freedom] moved on to more unique schlieren setups. One of these replaced the magnifying lens with a standard camera lens in which the aperture diaphragm replaced the razor blade, and another replaced the light source and razor with a high-contrast black-and-white pattern on a screen. The most sensitive technique was what he called double-pinhole schlieren photography, which used a pinhole for the light source and another pinhole in place of the razor blade. This could image the heated air rising from his hand, even at room temperature.

The high-contrast background imaging system is reminiscent of this technique, which uses a camera and a known background to compute schlieren images. If you’re interested in a more detailed look, we’ve covered schlieren photography in depth before.

Thanks to [kooshi] for the tip!

Budget Schlieren Imaging Setup Uses 3D Printing To Reveal The Unseen

April 17, 2025 by Tyler August 9 Comments

We’re suckers here for projects that let you see the unseeable, and [Ayden Wardell Aerospace] provides that on a budget with their $30 Schlieren Imaging Setup. The unseeable in question is differences in air density– or, more precisely, differences in the refractive index of the fluid the imaging set up makes use of, in this case air. Think of how you can see waves of “heat” on a warm day– that’s lower-density hot air refracting light as it rises. Schlieren photography takes advantage of this, allowing to analyze fluid flows– for example, the mach cones in a DIY rocket nozzle, which is what got [Ayden Wardell Aerospace] interested in the technique.

Shock diamonds from a homemade rocket nozzle imaged by this setup. — Examining exhaust makes this a useful tool for [Aerospace].

This is a ‘classic’ mirror-and-lamp Schlieren set up. You put the system you wish to film near the focal plane of a spherical mirror, and camera and light source out at twice the focal distance. Rays deflected by changes in refractive index miss the camera– usually one places a razor blade precisely to block them, but [Ayden] found that when using a smart phone that was unnecessary, which shocked this author.

While it is possible that [Ayden Wardell Aerospace] has technically constructed a shadowgraph, they claim that carefully positioning the smartphone allows the sharp edge of the case to replace the razor blade. A shadowgraph, which shows the second derivative of density, is a perfectly valid technique for flow visualization, and is superior to Schlieren photography in some circumstances– when looking at shock waves, for example.

Regardless, the great thing about this project is that [Ayden Wardell Aerospace] provides us with STLs for the mirror and smartphone mounting, as well as providing a BOM and a clear instructional video. Rather than arguing in the comments if this is “truly” Schlieren imaging, grab a mirror, extrude some filament, and test it for yourself!

There are many ways to do Schlieren images. We’ve highighted background-oriented techniques, and seen how to do it with a moiré pattern, or even a selfie stick. Still, this is the first time 3D printing has gotten involved and the build video below is quick and worth watching for those sweet, sweet Schlieren images. Continue reading “Budget Schlieren Imaging Setup Uses 3D Printing To Reveal The Unseen” →

On the left side, there's a smartphone. On the right side, there's a hairdryer turned on. On the smartphone screen, you can see the working end of the hairdryer shown, as well as a jet of air coming out of that end. In the background, there's an LCD screen showing a noise pattern.

Observe Airflow Using Smartphone And Background-Oriented Schlieren

July 17, 2022 by Arya Voronova 22 Comments

Multiple people have recently shared this exciting demonstration (nitter) with us – visualizing airflow using a smartphone, called ‘background-oriented schlieren’. On a hot summer day, you might see waves in the air – caused by air changing density as it warms up, and therefore refracting the light differently. Schlieren photography is an general set of techniques for visualizing fluid flow, but of course, it can also be applied to airflow. In this case, using some clever optical recognition tricks, this schlieren method lets you visualize flow of air using only your Android smartphone’s high resolution camera and a known-pattern printed background! Continue reading “Observe Airflow Using Smartphone And Background-Oriented Schlieren” →

Helicopter Is Full Of Compressed Air

April 27, 2021 by Al Williams 14 Comments

[Tom] likes to build little helicopters and decided to build one that runs on compressed air. (Video, embedded below.) Turns out it was a little harder than he thought. Originally, he was trying for a compressed air quadcopter. He’d already worked with an air turbine, but putting on a vehicle that can lift itself into the air turns out to have a lot of hidden gotchas.

[Tom] went through a lot of design considerations to arrive at the helicopter design. He considered counter-rotating props, but there were a host of problems involved. He finally settled on a single prob with a tail rotor that resides on the far end of a long boom to allow the resulting lever arm to reduce the work required of the tail rotor.

Continue reading “Helicopter Is Full Of Compressed Air” →

Hacklet 90: Schlieren Videos And Jigsaw Puzzle Robots

January 9, 2016 by Adam Fabio 2 Comments

Happy new year, and welcome to the first Hacklet of 2016! The Hacklet is one of my favorite columns to write, as I get to talk about the great projects people are working on at Hackaday.io. Generally these articles follow a theme, but this being a new year, I’m going to try something new. As Hackaday’s community editor, I keep an eye on the new and updated projects feeds over on Hackaday.io. Every single week I see projects that surprise, impress, and inspire me. This week, I’m going to highlight a couple that I think are just freaking awesome.

[Jana Marie] created the Schlieren-Videography project. Schlieren photography is used to image changing densities in fluids and this includes capturing density changes in air. Super and Hypersonic wind tunnels often use this technique to show airflow around a test model. Outside of the wind tunnel, Schlieren is great for showing density changes due to heat or different gasses. That’s exactly what [Jana] is doing in this project.

There are several ways to create Schlieren images, everything from lasers, to diffraction gratings, to razor blades can be used. [Jana] is using a simple moiré pattern and a couple of video tricks to capture Schlieren video. A high density moiré pattern will appear to flicker as density changes bend the light from the moiré stripes. [Jana] simply takes a reference image, then subtracts that image from the live video. The result of the subtraction is the Schlieren images you see above. [Jana] did more than explain the technique she’s used to create the videos, she’s also uploaded a processing sketch which performs the video subtraction magic.

[Dan Royer] has a more domestic problem – his family loves starting jigsaw puzzles, but never seems to finish them. He’s decided to invite around 3 billion of his closest friends in the form of JigSolve, an internet connected jigsaw puzzle robot. JigSolve’s Cartesian platform is a CoreXY based design. [Dan] used CoreXY as a guideline, but designed and built the hardware himself. The electronic hardware side borrows from RepRap 3D printers. An Arduino Mega2560 and RAMPS board control two NEMA 17 stepper motors. The Arduino is running firmware from Makelangelo, [Dan’s] own open source art robot.

The internet connected portion of the project comes in the form of a Java based IRC bot and a connection to the Freenode IRC network. The internet connected masses will have to see what they are working on, so a Logitech webcam will stream video to the ‘net.

The hardest part of JigSolve thus far has been the nozzle. Much like an SMT pick and place machine, the nozzle needs to pick up parts with a vacuum, then rotate them to the desired orientation. [Dan] is looking at different kinds of silicon, and he’s asking for suggestions. Stop over on the project page and offer him a hand!

That’s it for this week’s Hacklet. As always, see you next week. Same hack time, same hack channel, bringing you the best of Hackaday.io!