lenses

Lenses are transparent optical elements with curved surfaces that refract light to form images. They are typically made of glass or plastic and rely on refraction to converge or diverge light rays. The shape and material determine focal length and aberrations.

Types of lenses include converging lenses (convex) that bend light toward the axis and can form real or virtual images depending on object distance, and diverging lenses (concave) that spread light and always form virtual images for real objects. Common shapes include biconvex, planoconvex, biconcave, and meniscus lenses. Lenses are described by focal length and principal planes using the lensmaker's equation.

Materials and coatings vary by application. Common lens materials include crown glass, flint glass, and plastics such as PMMA or polycarbonate. Refractive index and dispersion affect performance; coatings like anti-reflective and protective layers reduce losses and scratches.

Manufacturing and quality control involve grinding and polishing surfaces to precise curvature, followed by edge finishing and centering. Optical testing uses interferometry, spot tests, and lens testing to ensure curvature accuracy and surface smoothness.

Applications cover a wide range of devices and systems. Lenses are central to eyeglasses, cameras, microscopes, telescopes, projectors, and laser systems. They are used in consumer electronics, scientific instrumentation, and industrial optics, and may be designed for specific wavelengths and environments.

Variants and advances include aspheric designs to reduce aberrations, achromatic doublets to minimize chromatic aberration, and gradient-index or free-form surfaces for complex optical paths. Developments continue in lightweight materials and advanced coatings to improve performance and durability.