[―?]about point source~~~

稱叫毙???秈,и璶??磞酶??翴?方
и琌稱礶??翴?方??lens?focal point?,s.t程????キ︽optical axis

could someone tell me how to draw a point light source in a optical sys??
(I want draw a sys that light from a point source and pass a convex lens and cause a collimator light)