Caustic Lens Generator (Yunyi Zhu)

About this generator

The Caustic Lens Generator turns a grayscale image into a 3D-printable refractive lens. The lens has a flat top and a shaped relief underneath. When sunlight passes through the clear print, the relief bends the light into a bright copy of your image on a surface held at the focal distance you chose. It is based on a 2014 research paper on caustic design, and the maker, Yunyi Zhu of MIT, built it to draw images on photochromic sheets with the sun.

You drop in an image, which is cropped to a square, and set the lens size, focal distance and base thickness, with an option to invert it. The mesh resolution and the number of solver sites decide how much detail survives: the page says the recommended print settings take about 8 to 12 minutes in the browser, while the preview settings finish in about a minute but only keep coarse shapes. The result panel shows a height map, the footprint, total height and relief depth, and warns when the relief punches through the flat face. A link opens an outside ray-tracing simulator to preview the light pattern.

The download is an OBJ in millimeters. The guide says to print it in clear resin, polish it and place the target surface at the focal distance below the relief. It is free, needs no account and runs entirely in the browser, so nothing is uploaded. The source code is public on GitHub, but the repository has no license file. It suits makers with a resin printer who want an unusual print that shows a picture only in the right light.

What you can make

• Caustic lenses that project an image in sunlight
• Lenses from 5 to 200 mm across
• Light-drawing lenses for photochromic sheets

How to use Caustic Lens Generator

1. Drop in a grayscale image with clear bright shapes
2. Set the lens size, focal distance and base thickness
3. Generate at preview settings first, then at print settings
4. Download the OBJ, print it in clear resin and polish it