Gravitational lensing as folds in the sky

We revisit the gravitational lensing phenomenon using a new visualization t echnique. It consists in projecting the observers sky into the source plane , what gives rise to a folded and stretched surface. This provides a clear graphical tool to visualize some interesting well-known effects, such as th e development of multiple images of a source, the structure of the caustic curves, the parity of the images and their magnification as a function of t he source position.