Conceptually, a camera lens isn't a complicated piece of kit. Still, the quality of images photographer Mathieu Stern managed to take with his 3D-printed lens, featuring a single front element and mounted on his Sony Alpha 7ii, is still surprising. Only the blur and distortion in the corners gives the game away.
The photographer estimates the lens is equivalent to a 135mm f/1.8 device, though you can be the judge:
I'm sure the high-resolution raw images would reveal plenty of defects, but the photos are more than fine, all things considered. I doubt it's something you'd take on serious snapping sessions -- who knows what the build quality is like -- but it's a great experiment.