Polttovälinä

Polttovälinä, known in English as the focal length, is a fundamental concept in optics that describes the distance between the optical lens or mirror and the point where parallel rays of light converge or appear to diverge, known as the focus. It is a key parameter in determining the optical properties of lenses and mirrors, influencing magnification, field of view, and image formation.

The focal length is typically expressed in millimeters or centimeters and varies depending on the curvature and refractive index of the lens or the shape of the mirror. A lens with a short focal length has a wide field of view and produces a more magnified image, making it suitable for close-up or wide-angle photography. Conversely, a longer focal length provides a narrower view and greater magnification, often used in telephoto lenses for distant subjects.

In photographic and optical applications, the focal length also affects the perspective and distortion within an image. Shorter focal lengths tend to exaggerate the depth and distance between objects, while longer focal lengths compress the spatial relationship, providing a flatter appearance.

The calculation of focal length depends on the lens' geometry and material properties and can be derived through optical formulas or measured directly using optical testing equipment. The concept originates from geometrical optics principles and is essential for designing optical systems in cameras, microscopes, telescopes, and other devices.

Understanding the focal length helps in choosing appropriate optical components to achieve desired imaging results, making it a core concept in both scientific and practical applications of optics.