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!

Light Transport And Constructing Images From A Projector’s Point Of View

August 7, 2025 by Lewin Day 6 Comments

Imagine you have a projector pointing at a scene, which you’re photographing with a camera aimed from a different point. Using the techniques of modelling light transport, [okooptics] has shown us how you can capture an image from the projector’s point of view, instead of the camera—and even synthetically light the scene however you might like.

The test scene used for the explanation of the work.

The concept involves capturing data regarding how light is transported from the projector to the scene. This could be achieved by lighting one pixel of the projector at a time while capturing an image with the camera. However, even for a low-resolution projector, of say 256×256 pixels, this would require capturing 65536 individual images, and take a very long time. Instead, [okooptics] explains how the same task can be achieved by using binary coded images with the projector, which allow the same data to be captured using just seventeen exposures.

Once armed with this light transport data, it’s possible to do wild tricks. You can synthetically light the scene, as if the projector were displaying any novel lighting pattern of your choice. You can also construct a simulated photo taken from the projector’s perspective, and even do some rudimentary depth reconstruction. [okooptics] explains this tricky subject well, using visual demonstrations to indicate how it all works.

The work was inspired by the “Dual Photography” paper published at SIGGRAPH some time ago, a conference that continues to produce outrageously interesting work to this day.

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19th Century Photography In Extreme Miniature

June 29, 2025 by Bryan Cockfield 10 Comments

Ever since the invention of the microscope, humanity has gained access to the world of the incredibly small. Scientists discovered that creatures never known to exist before are alive in an uncountable number in spaces as small as the head of a pin. But the microscope unlocked some interesting forms of art as well. Not only could people view and photograph small objects with them, but in the mid-nineteenth century, various artists and scientists used them to shrink photographs themselves down into the world of the microscopic. This article goes into depth on how one man from this era invented the art form known as microphotography.

Compared to photomicroscopy, which uses a microscope or other similar optical device to take normal-sized photographs of incredibly small things, microphotography takes the reverse approach of taking pictures of normal-sized things and shrinking them down to small sizes. [John Benjamin Dancer] was the inventor of this method, which used optics to shrink an image to a small size. The pictures were developed onto photosensitive media just like normal-sized photographs. Not only were these unique pieces of art, which developed — no pun intended — into a large fad, but they also had plenty of other uses as well. For example, since the photographs weren’t at all obvious without a microscope, they found plenty of uses in espionage and erotica.

Although the uses for microphotography have declined in today’s digital world, there are still plenty of unique pieces of art around with these minuscule photographs, as well as a bustling collector culture around preserving some of the antique and historical microphotographs from before the turn of the century. There is also similar technology, like microfilm and microfiche, that were generally used to preserve data instead of creating art, although plenty of these are being converted to digital information storage now.

Projector on left with red arrow pointing towards object, another red arrow points towards a piece of paper and then camera.

Pictures From Paper Reflections And A Single Pixel

June 29, 2025 by Ian Bos 25 Comments

Taking a picture with a single photoresistor is a brain-breaking idea. But go deeper and imagine taking that same picture with the same photoresistor, but without even facing the object. [Jon Bumstead] did exactly that with compressed sensing and a projector. Incredibly, the resulting image is from the perspective of the projector, not the “camera”.

This camera setup is very similar to one we’ve seen before, but far more capable. The only required electronics are a small projector and a single photodiode. The secret sauce in this particular design lies in the pattern projected and the algorithm to parse the data.

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Close up of a custom optical HDMI cable on a desk

Let There Be Light: The Engineering Of Optical HDMI

February 18, 2025 by Heidi Ulrich 15 Comments

In a recent video, [Shahriar] from The Signal Path has unveiled the intricate design and architecture of optical HDMI cables, offering a cost-effective solution to extend HDMI 2.0 connections beyond the limitations of traditional copper links. This exploration is particularly captivating for those passionate about innovative hardware hacks and signal transmission technologies.

[Shahriar] begins by dissecting the fundamentals of HDMI high-speed data transmission, focusing on the Transition Minimized Differential Signaling (TMDS) standard. He then transitions to the challenges of converting from twisted-pair copper to optical lanes, emphasizing the pivotal roles of Vertical-Cavity Surface-Emitting Lasers (VCSELs) and PIN photodiodes. These components are essential for transforming electrical signals into optical ones and vice versa, enabling data transmission over greater distances without significant signal degradation.

A standout aspect of this teardown is the detailed examination of the optical modules, highlighting the use of free-space optics and optical confinement techniques with lasers and detectors. [Shahriar] captures the eye diagram of the received high-speed lane and confirms the VCSELs’ optical wavelength at 850 nm. Additionally, he provides a microscopic inspection of the TX and RX chips, revealing the intricate VCSEL and photodetector arrays. His thorough analysis offers invaluable insights into the electronic architecture of optical HDMI cables, shedding light on the complexities of signal integrity and the innovative solutions employed to overcome them.

For enthusiasts eager to take a deeper look into the nuances of optical HDMI technology, [Shahriar]’s comprehensive teardown serves as an excellent resource. It not only gives an insight in the components and design choices involved, but also inspires further exploration into enhancing data transmission methods.

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A Waist Level Viewfinder For Not A Lot

January 26, 2025 by Jenny List 8 Comments

Photographic accessories are often plagued by high prices, as photography is considered a rich man’s game. It doesn’t have to be that way though, and [Snappiness] is here to get you started on the route to cheaper kit with a waist-level viewfinder project.

If you’ve used a twin-lens reflex camera then you should be familiar with a waist level viewfinder, it’s a lens and mirror arrangement allowing the photographer to frame the shot looking down from above. Modern cameras often have no viewfinder, so this is aimed at digital compacts without flip-up screens.

It has three components, all available for relatively low prices, and mounted in a 3D printed case. There’s a prime lens, a mirror, and a Fresnel lens forming the part the photographer looks through. It’s a simple device, but still one which would cost a lot more off the shelf. The video is below the break.

It might interest you to know that this is not the first viewfinder project we’ve brought you for digital cameras.

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Schematic of quantum measurement basis on whiteboard

Shedding Light On Quantum Measurement With Calcite

January 26, 2025 by Heidi Ulrich 19 Comments

Have you ever struggled with the concept of quantum measurement, feeling it’s unnecessarily abstract? You’re not alone. Enter this guide by [Mithuna] from Looking Glass Universe, where she circles back on the concept of measurement basis in quantum mechanics using a rather simple piece of calcite crystal. We wrote about similar endeavours in reflection on Shanni Prutchi’s talk at the Hackaday SuperConference in 2015. If that memory got a bit dusty in your mind, here’s a quick course to make things click again.

In essence, calcite splits a beam of light into two dots based on polarization. By aligning filters and rotating angles, you can observe how light behaves when forced into ‘choices’. The dots you see are a direct representation of the light’s polarization states. Now this isn’t just a neat trick for photons; it’s a practical window into the probability-driven nature of quantum systems.

Even with just one photon passing through per second, the calcite setup demonstrates how light ‘chooses’ a path, revealing the probabilistic essence of quantum mechanics. Using common materials (laser pointers, polarizing filters, and calcite), anyone can reproduce this experiment at home.

If this sparks curiosity, explore Hackaday’s archives for quantum mechanics. Or just find yourself a good slice of calcite online, steal the laser pointer from your cat’s toy bin, and get going!

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