bikonvex

A bi-convex lens, also spelled biconvex, is a lens with two outward-curved surfaces. It is a convex lens that converges light and is commonly used in optical systems to form real or magnified images.

In its symmetrical form, the two surfaces have equal radii of curvature, producing a balanced optical element. Variants with unequal radii exist and can tailor aberration correction for specific applications. Some designs also employ aspheric surfaces to reduce spherical aberration and improve image sharpness.

Optical properties are described by the lensmaker’s equation. For a thin bi-convex lens with equal radii R and refractive index n, the focal length f approaches R divided by 2(n−1). The lens’s optical power is the reciprocal of the focal length. The exact performance depends on thickness, curvatures, material, and coatings, and real lenses may require more detailed modelling for aberrations.

Materials commonly used include crown glass and other optical glasses, as well as plastics such as PMMA and polycarbonate. Plastics offer lighter weight and easier manufacturing for some applications, while glasses can provide higher refractive indices and better environmental stability.Anti-reflective or protective coatings are often applied to improve transmission and durability.

Manufacturing involves precision grinding and polishing of two convex surfaces, followed by edge thinning, mounting, and coating. Tolerances on radii, centering, and surface smoothness determine image quality and are critical for high-performance optics.

Applications of bi-convex lenses include eyeglasses for correcting farsightedness, camera and projector lenses, and various scientific instruments. Related topics include other lens shapes such as planoconvex and biconcave lenses, and the lensmaker’s equation.