kaksoislinssistä

Kaksoislinssi, or doublet lens in English, is an optical lens assembly consisting of two individual lenses. These lenses are typically made of different types of glass, such as crown glass and flint glass, and are cemented or air-spaced together. The primary purpose of a double lens is to correct for optical aberrations, most notably chromatic aberration.

Chromatic aberration occurs because different wavelengths of light are refracted at slightly different angles when passing through a single lens. This results in a visible spectrum of colors around the image, reducing its sharpness. By combining lenses made of materials with different dispersive properties, a doublet lens can bring two specific wavelengths of light to the same focal point. This significantly reduces the color fringing observed in images.

The design of a doublet lens involves careful selection of lens shapes (e.g., plano-convex, biconvex, plano-concave, biconcave) and the refractive indices and Abbe numbers of the glass used for each element. The goal is to achieve apochromatic correction, where three wavelengths are brought to focus, or at least achromatic correction, where two wavelengths are focused. Doublet lenses are widely used in various optical instruments, including telescopes, microscopes, camera lenses, and binoculars, to improve image quality.