You will hear about the term focal length, in respect to lenses quite often. Unlike some misconceptions focal length is not the measurement of the lens. It is in fact a measurement in millimeters of the distance between the point where light rays converge after traveling through the lens and the image medium (sensor / film / wet plate). Depending on this distance you can tell a lot about the type of lens it is, the amount of image magnification you can hope to achieve and how big the subjects will appear on the image plane. Shorter the focal length, wider the angle of view of the lens. e.g., an 18mm lens has a much wider field of view than a 200mm lens. The subjects in the image will appear very small (depending on where they are stand). On the other hand, a telephoto lens has a very small field of view. But, objects in the image will appear very close. Resultantly the magnification is bigger when using a tele-lens. The actual focal length does not change regardless of whether it designed for full-frame cameras or for smaller APS-C cameras.
Focal lengths of lenses are segregated into three basic groups. Wide, standard and telephoto. They are further divided into separate sub-groups. Wide (primes such as the Nikkor 24mm f/2.8), ultra-wide (primes such as the Nikkor 14mm f/2.8), wide-zoom, standard-zoom (such as the Nikkor 18-55mm f/3.5 – 5.6, standard, telephoto (like the Nikkor 200mm f/2) and super-telephoto (like the 500mm f/4). Zoom lenses are those which have a variable focal length like the Nikkor 200-400mm f/4 VR II. Primes are fixed focal length lenses and have only a fixed focal length. The subject of your photography will determine the kind of focal length that you should be using. Landscape photography requires a wide angle lens. Architecture photos require an ultra-wide angle lens. Wildlife, sports and action photos will need telephoto and super-telephoto lenses. Standard lenses are general purpose and can be used for everyday photography needs such as weddings, capturing family group shots, vacations and doing street photography.« Back to Glossary Index