Bi-convex lenses

The convex surfaces of these lenses are symmetric with the focal length equal to the radius of curvature. Because of their symmetric shape they have good performance for imaging close to 1 and magnifications from 5 to 0,2. Another advantage over plano convex lenses is a shorter focal length at higher aperture ratio (because both convex surfaces contribute to the magnifying power). Choose one of these lenses for beam focussing for a short optical path, particularly where image quality or spot size is not critical.