Plano Concave Lens

Plano concave lens bend parallel input rays so they diverge from one another on the output side of the lens and hence have a negative focal length. The spherical aberration of the plano concave lenses is negative and can be used to balance aberrations created by other lenses. Similar to the plano concave lens, the curvature surface usually faces the largest object distance or the infinite conjugate to minimize spherical aberration.