1. The problem statement, all variables and given/known data A monochromatic source of light 'S' is placed at the principal focus of a convex lens 'L1'. A parallel beam of light or a plane wave front is incident on the narrow slit represented by AB (its width - 'a') 2. Relevant equations So, what my teacher did was, She showed diffraction of the light rays as they pass through the slit. And then she made the rays to meet at a point 'P'. Look at the image. Doesn't the convex lens L2 seem to be actually 'diverging' the rays? Shouldn't it 'converge' them? I'm literally confused about it, because all the books seem to support my teacher.