Patent ID: 6317272
Filing Date: 2001-11-13
Classification: G02B

Abstract:
A zoom lens formed of no more than four lens groups having refractive power, in order from the object side, as follows:a first lens group that is fixed in position and has positive refractive power;a second lens group having negative refractive power, the position of the second lens group being variable along the optical axis in order to change the focal length of the zoom lens, said second lens group including, in order from the object side, a negative lens element having a concave surface or a planar surface on its object side, and a combined lens which includes a biconcave lens element joined to a positive meniscus lens element with its convex surface on the object side;a third lens group that is fixed in position and has positive refractive power, said third lens group consisting of a single lens element with at least one surface thereof being aspherical; and,a fourth lens group having positive refractive power and including a lens element having an aspherical surface, the position of the fourth lens group being variable along the optical axis in order to compensate for what would otherwise be movement of the image plane due to changes in the amount of zoom and the object distance.