sentences:  A lens is considered to be a "normal lens", in terms of its angle of view on a camera, when its focal length is approximately equal to the diagonal dimension of the film format or image sensor format.The resulting diagonal angle of view of about 53 degrees is often said to approximate the angle of human vision; since the angle of view of a human eye is at least 140 degrees, more careful authors will qualify that, for example as "similar to the angle of crisp human vision.