Lenses with variable focus allow the focal length to be adjusted within a certain range. A change of the focal length changes also the angle of view. A shorter focal length leads to a wider angle of view, whereas lenses with a long focal length cover only a limited angle of view.

The Angle of view of the human eye is approx. 33.4 degree, which corresponds to a focal length of 8mm. Larger Angle of views are often designated as “wide angle”. Lenses with smaller angles of views are sometimes called “Tele”.