Algorithms for tracking targets imaged through a zoom lens must accommodate changes in the magnification of the target. This requirement poses particular problems for correlation techniques, which usually are not invariant to scale changes. An adaptive correlation method has been developed that selectively updates the correlation template in response to scale changes in an image sequence. The algorithm estimates a subset of the parameters of the affine transformation between the template and the matched image patch and updates the template only when the scaling exceeds given bounds. The selective template update enables correlation to track targets at varying scale while decreasing the risk of template drift.