This paper discusses the motion estimation problem of a rigid-body using a zoom camera via observations of a single feature point. Both the rotational and translational parameters are assumed to be unknown constants. Estimation of the unknown parameters is obtained in two steps. In the first step, the camera's focal length is fixed and the rotational parameters can be estimated. In the second step, the camera's focal length is changing as a time-varying signal. In our current design, the focal length performs a sinusoidal motion. The unknown depth, along with the translational parameters, can be estimated. Simulation results are presented that demonstrate successful motion estimation.