I recently stumbled upon caustic lenses through this video by Steve Mould and immediately knew that I had to integrate these into a project. Naturally

Caustic Clock : 6 Steps - Instructables

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2025-01-20 10:00:14

I recently stumbled upon caustic lenses through this video by Steve Mould and immediately knew that I had to integrate these into a project. Naturally, this would be another clock and I had different concepts in mind. I already knew about the wonderful hollow clocks by shiura and thought pairing these with a caustic lens would be a perfect match. Originally, I just wanted to put the clock next to the window and have sunlight passing through the lens but I ended up making a small projector using an RGB LED that can be put in front of the clock so that you can also see the image at night.

Calculating the surface of a caustic lens that will project a random image is a non-trivial task. Probably the most sophisticated algorithm for this comes from researchers at EPFL. Luckily, I found this github repo by Matt Ferraro that also does the job using a slightly different algorithm. I made some minor modifications to his code (see my github) in order to be able to try out different focal lengths and refractive indices. The code generates an obj file which was then edited in Fusion360 in order to make a round lens instead of a square one and the file was exported as stl.

How do you know that the lens you created is really projecting the image that you want? To test this I used the LuxCore Render in Blender to make a ray tracing simulation. It was really satisfying to see the correctly projected image in the ray tracing simulation.