What Leonardo da Vinci invention was designed to grind lenses?

Leonardo da Vinci designed a lens-grinding machine for shaping optical lenses.

The mechanism used rotary motion and adjustable components to help grind and polish curved glass surfaces. Leonardo’s interest in optics connected his mechanical studies with investigations of vision, light, perspective, and the structure of the eye. Producing accurate curved lenses required controlled abrasion and careful shaping, making it a suitable problem for his engineering notebooks.

This machine should not be confused with an invention of the telescope or microscope. Leonardo investigated optical instruments and visual phenomena, but surviving evidence does not establish that he built a modern version of either instrument. His lens-grinding design is significant because it shows how he approached precision manufacturing through mechanical control.