An outline of how the dark matter distribution (right) was reconstructed from optical images (left) taken by the Subaru Telescope. A precise measurement of the shapes of background galaxies in observed images enabled the team to investigate the distortion pattern (center) and then reconstruct the distribution of dark matter in the galaxy clusters. // NAOJ/ASIAA/School of Physics and Astronomy, University of Birmingham/Kavli IPMU/Astronomical Institute, Tohoku University