Polttopistepituudet

Polttopistepituudet refers to the focal lengths of lenses, a fundamental concept in optics. It is the distance from the optical center of a lens to its principal focus, where parallel rays of light converge after passing through a converging lens, or appear to diverge from after passing through a diverging lens.

This measurement is crucial for understanding how a lens magnifies or reduces images and how it focuses light. A shorter focal length indicates a stronger lens that bends light more sharply, resulting in a wider field of view and greater magnification. Conversely, a longer focal length signifies a weaker lens that bends light less, leading to a narrower field of view and less magnification.

In photography, the focal length of a camera lens determines the angle of view and the magnification of the subject. Wide-angle lenses have short focal lengths, capturing a broad scene, while telephoto lenses have long focal lengths, bringing distant objects closer.

In eyeglasses, the focal length of the lenses is prescribed to correct refractive errors like myopia (nearsightedness) and hyperopia (farsightedness). For myopia, diverging lenses with negative focal lengths are used, while converging lenses with positive focal lengths correct hyperopia.

The unit of measurement for focal length is typically millimeters (mm) or meters (m). The reciprocal of the focal length, measured in diopters, is often used to express the refractive power of a lens, particularly in optometry.