Plano convex lenses

Plano convex lenses are the most basic optical elements. They have positive focal lengths and close to the optimum shape for use as collimating condensers and as focussing lenses for collimated beams.The orientation of the lenses within the optical system is critical to the image quality. They have low spherical aberration if the lens is orientated in such a way that the collimated beam enters or leaves from the curved side so the plano side faces the focus or point source.