planoconvex

Planoconvex, or plano-convex, describes an optical lens with one flat surface and one outward-facing spherical surface. The curved surface has a radius of curvature R, while the plane face is flat. In the thin-lens approximation, the focal length f is approximately f = R/(n−1), where n is the refractive index of the lens material. The orientation of the curved surface affects aberrations, and plano-convex lenses are commonly used to focus light from distant sources. They are often configured with the curved side facing the incoming light to help minimize spherical aberration for a given focal length, though exact performance depends on thickness, wavelength, and mounting.

Materials and manufacture: Plano-convex lenses are made from glass types such as BK7, F2, or fused silica, as well as optical plastics like acrylic. They are produced by grinding and polishing to the specified curvature, followed by edge finishing and anti-reflective coatings to improve transmission and image quality. Tolerances on diameter, thickness, and surface accuracy are specified for precision applications.

Applications: They serve in a variety of optical systems, including imaging lenses, projection optics, laser beam focusing and collimation, and optical coupling into fibers or detectors. Their simple shape, relatively low cost, and good performance for collimated or nearly collimated light make them a common choice in educational setups and commercial instruments.

Variants and considerations: Planoconvex lenses are available with different radii and clear apertures, and may be mounted in various housings. Designers select curvature, material, and coating to balance focal length, aberrations, and transmission for the intended wavelength range.