This is a version of Ella's / Brent's Bahtinov mask which I modified for the famous Samyang 135mm F/2 lens. I implemented a pretty narrow pattern (0.8mm) for a large diffraction pattern.
First tests proved it's working as expected as you can see from the three focus screenshots:
Left: intrafocal, Middle: focal, Right: extrafocal
The project's source code is now hosted at Github:
I ordered the mask at MeltWerk. They produce all things in PA12 using SLS (Selective Laser Sintering). The fine bars of 0.8mm were the absolute manufacturing limit according to their specification.