Strange, I thought there is nothing to focus about lasers, after all those are in-phase, rectilinear beams with extremely low dispersion!? Could it be the so called focus procedure is rather an alignment process to insure the three laser spots overlap?
It's unlikely that the width of the beam at its source is going to be exactly the same size as the desired spot size on the paper. Hence focussing is required to change the size.
S
