Fokuspituus

Fokuspituus, often translated as focal length, is a fundamental parameter in optics and photography. It describes the distance between the optical center of a lens or mirror and its focal point. The focal point is the point where parallel rays of light converge after passing through a lens or reflecting off a mirror.

In simple terms, fokuspituus determines the field of view and magnification of an optical system. A shorter fokuspituus results in a wider field of view, capturing more of the scene, and is characteristic of wide-angle lenses. Conversely, a longer fokuspituus yields a narrower field of view and greater magnification, making distant objects appear closer, and is typical of telephoto lenses.

For cameras, fokuspituus is measured in millimeters (mm) and is a key specification that influences the perspective and composition of an image. It is directly related to the size of the image sensor. For instance, a 50mm lens on a full-frame camera is considered a "normal" lens, offering a perspective similar to human vision. On a smaller sensor, the effective focal length will be different due to a crop factor, requiring a shorter actual focal length to achieve the same field of view. Understanding fokuspituus is crucial for photographers and optical engineers to select appropriate lenses and design optical instruments.