The lenses adjusted back and forth of the instrument include convex lens and concave lens.

The lenses adjusted before and after the laser beam expander are convex lens and concave lens respectively. The convex lens has the function of converging light and can make the laser beam thinner. The concave lens can scatter light and make the laser beam wider.

These lenses can be adjusted by rotating or moving their positions to obtain the required laser beam shape and size.