Camera + monitor video feedback loop awesomeness

Updated: May 16, 2015

Don't forget to check the awesome video clip later in the article!

Today, I would like to run a very neat physics experiment with you, and it also comes with some lovely footage. Let's begin with a sort of troll physics question. If you connect a video camera to a monitor and then point the camera at the monitor, what will happen? Since you will effectively be projecting your own video onto the monitor, the process will repeat itself infinitely, and you will win infinite photons.

On a more serious level, this cool phenomenon is our topic today, and we will discuss the why and how behind it. How does this nice thing work, and why you should care? Anyhow, we will touch upon the topic of strange loops, recursion, fractals, all sorts of physical effects, and more. Follow me.


Experiment setup

I have read lots of articles on the topic, and none really satisfied me. So I'm going to give you my own version, and my own unique analogies. First, let's begin with a static image. This is called the Droste Effect, and it features a picture appearing within itself recursively. Theoretically, the recursion is infinite, and goes beyond the limits of known physics, once you hit the Planck unit size. In reality, the iterations end, or break, once you reach the lower representation unit available, be it the pixel on a digital screen, a canvas molecule, paint or ink droplet size, the ability of your eye to resolve details, and so forth.

Now, what happens if you put the Droste Effect into motion? In other words, turn a static image into a living picture captured by a video camera? Indeed, this is what I did. First, I tried using my Canon IXUS device for the experiment, but its mini-HDMI port only allows output of captured files. Then, I hooked in my GoPro to the LG TV, and this worked seamlessly. For best effect, I narrowed down the viewing field of the camera to show only the television set and its stand. I held the camera by hand, although you can use all kinds of mounts and pivots. Either way, you will get some spectacular results, as the video below shows.

The demo!

Indeed, since you asked:

Most Awesome, is it not? Now, let's discuss why this is so.

Video feedback explained

This thing comes with some pretty tricky mathematics. But the simplest, most fun way to treat this lovely phenomenon is as a chain of links. Each displayed video frame is one link. The first time you point an active camera lens at the monitor to which it is connected, there's an ever so slight delay that it takes to display the information. This time delay, incurred by the camera sensor processing, creates a temporal disturbance, which propagates through the system.

The disturbance travels outwards toward the monitor so the speak, or you may look at it as if the original picture is getting farther and farther away, and indeed, each successive loop cycle moves the initial projection from the display by the same distance, caused by the feedback time delay. If you also change the camera angle, zoom and position, you add a third dimension to the equation, and you introduce an additional perturbation into the system.

Example of temporal perturbance

If you look at the sample screenshot, the time stamp of the recording is the best indication and measurement of the actual temporal disturbance. Roughly a second elapses for every four projections, which means the system takes about 250ms to respond, or roughly 7-8 video frames at 30fps recording. Therefore, if a typical 1080p screen can project roughly 50 loop iterations, if you shake the camera, move it, or rotate it, it will take approximately ten or eleven seconds for the change to reach the last visible iteration. Of course, the system depth continuously growths, but the camera and the monitor are no longer able to record the information, and the digital data is compressed to a single bit. Singularity. Coolness galore.

This is very much like a rope or chain. If you shake it vertically, the perturbation will advance as a wave front horizontally, along the chain. This means any change in the displayed projection translates into a change in the video, which can sometimes take crazy, psychedelic shapes. Moreover, what makes this whole experiment extra rad is that self-referencing systems and strange loops phenomena are an integral part of the wondrous world of fractal geometry. If you're really interested, this PDF from 1984 (direct link, mind), explains it all.

Wave front

Effectively, this means that with the right lighting conditions, camera equipment and your ability to estimate the time delay, you can try creating art, making interesting and beautiful shapes, spirals, circles, and whatnot. It's entirely up to you. I did my best in the few minutes of recording and playing, but I challenge you to do better and post your own video response to my experiment. Wait, who am I kidding? Since when did I partake in this whole gushy social sharing stuff? Never. Do as you please.


This is a very cool thing, you must admit. Self-referencing systems are the blast, and when you add recursion, your mind goes on a wild tangent. But what really makes the experiment particularly interesting is that by using digital equipment, you can simulate natural occurring phenomena in the nature. Fractals do deserve their respect. Which begs the question, why patterns align in a fractal fashion? And can we use cameras to detect a hidden truth in the geometric order around us?

At the very least, even if we cannot immediately answer these questions, we can have some innocent fun. I truly hope you find this little work enlightening and entertaining, perhaps at the same time. In fact, I suggest you try this at home. Yes, do try this at home. If you have any ideas for other physics experiments, please feel free to ping me. That would be.