Refractography is recording video without a lens and viewing the caustics directly

Caustics occur when photons are refracted by an object and form strange patterns of concentrated light. The physics that we live within are capable of incredible complexity from simple initial conditions. I’m not sure why but I’ve long been entranced by these ethereal lights. Even as a kid I loved the light patterns on the bottom of a pool and glass objects in sunlight. So let’s capture some physical caustics with a lensless camera. Practical effects, no 3D renders here!

Recording video of caustics is a delicate business. In the photography community this technique is known as refractography. A while back I stumbled across the work of [Shawn Knol](https://www.instagram.com/extraouterordinary/), who has mastered the technique of creating caustics by using both glass or liquids. His artwork is beautiful and I hope to experience one of his short films on a big screen someday. Luckily over on his Reddit profile he has shared bits and pieces of knowledge for how he records video of caustics. Much respect! Along with a few tutorials ([Abstract Photography with No Lens](https://www.youtube.com/watch?v=ZmzPTwQjY-E) and [How To Make Refractographs](https://www.youtube.com/watch?v=qRVPWPAGG54)) and from there I was able to cobble together an understanding of the technique. The basic physical setup is: tungsten spotlight >>> pinhole >>> glass object on turntable >>> lensless camera

The idea here is to make a pseudo camera obscura, except in this case I’m not projecting an image… I’m visualizing the diffracted photons. So by passing the light through a pinhole, it becomes collimated and most of the light rays are parallel. Then the collimated light is pointed into a glass object where the light rays refract in bizarre ways. From there the light is pointed directly onto a camera sensor. In this way, no lens is needed since the pinhole lighting rig focuses the light and the glass object distorts the light. Due to the requirement of using a pinhole light source, the light is therefore quite dim and so I had to record at night since I didn’t want any stray light affecting the setup. Also in my experience the caustics look best when the camera sensor is 1 to 4 inches from the glass object. So projecting the light onto a wall becomes too challenging in multiple ways. But luckily modern video camera sensors are incredibly sensitive and so projecting the refracted light directly onto the camera sensor is ideal in this setup.

I used a tungsten spotlight in this project for a few reasons. The drawback of tungsten lights is that they get extremely hot. And while I’d much rather use a LED spotlight, it’s def not ideal in this context. Primarily because an LED spotlight is commonly made up of hundreds of small LED light sources that together work to make the appearance of a single light source. I did a preliminary test using my wife’s Godox SL-60W LED spotlight and when a pinhole is placed directly in front of the LED spotlight, then you can see the individual LED light sources in the projected image… Just like a camera obscura. Therefore I needed to use a tungsten spotlight so that I could have a true single light source. Secondarily because an LED spotlight doesn’t output a full spectrum of light, which is important in the rainbows that are created when the light is refracted through the glass and dispersed. Honestly it wasn’t really a huge difference visually to my eyes, but it’s an added bonus of using a tungsten spotlight. Although I overlooked a detail and rented a tungsten light which had a fresnel lens attached (instead of being open face) which augmented the pinhole light to include the ridges of the fresnel lens. But I’m still pleased with the results.

To create the pinhole rig I grabbed one of the scrim frames that was included with the rented spotlight, covered it in a single layer of cinefoil, and then used a size 10 embroidery needle to puncture a hole through the middle of the cinefoil. There is a fine balance here since the smaller the diameter of the pinhole in the cinefoil then the sharper the projected image and yet the dimmer the overall luminosity of the projected light. Then I inserted the pinhole scrim into the spotlight and this allowed me to create near collimated light.

That is a truly captivating! Viewing the caustics directly is a stunning display of light and refraction.

Song: Boards of Canada – Peacock Tail

Holy shit this looks amazing! It looks like something that would be projected at a Nine Inch Nails concert. I need a screensaver of this.

Eh

Not dissimilar to how my vision changed during cataract surgery.

Saving this video for a friend that likes to get high.

Thank you. I see caustics through raindrops on glasses at night, eyelashes when squinting, etc, and had no idea this was so well recorded in other ways.