The Hubble Space Telescope's main mirror was ground to the wrong shape by 2.2 micrometers, about one-fiftieth the width of a human hair, and the error was only caught after launch because the device used to verify the mirror on the ground had itself been

The Hubble Space Telescope's main mirror was ground to the wrong shape by 2.2 micrometers, about one-fiftieth the width of a human hair, and the error was only caught after launch because the device used to verify the mirror on the ground had itself been

Hubble's primary mirror was polished to perfection, just to the wrong shape, because the device built to measure it had a chipped flake of paint that threw its internal geometry off by 1.3 millimeters. The mirror was checked against a ruler that was itself broken.