Gravitational lensing by point masses on regular grid points

It is shown that gravitational lensing by point masses arranged in an infinitely extended regular lattice can be studied (semi-)analytically. In particular, we draw the critical curves and the caustic networks for the lenses arranged in regular-polygonal - square, equilateral triangle, regular hexagon - grids. From this, the mean number of positive parity images as a function of the average optical depth is derived and compared to the case of the infinitely extended field of randomly distributed lenses. We find that the high degree of the symmetry in the lattice arrangement leads to a significant bias towards cancelling of the shear caused by the neighbouring lenses on a given lens position and lensing behaviour that is qualitatively distinct from the random star field. We also discuss some possible connections to more realistic lensing scenarios.