Plano-Concave Lens has a negative focal length and is typically used to cause a collimated beam to diverge as in a Galilean type beam expander or Telescope. Because the spherical aberration of the Plano-Concave is negative, it can be used to balance the aberration of other lenses.This lens is widely use in optical display systems, projection optics systems, imaging and laser measureemnt systerms.