Abstract: A novel technique for self-calibration of cameras with varying focal length is introduced.The aspect ratio and principal point can be estimated beforehand because they are changeless during camera movements.For zero-skew,a linear solution is derived by using the Huang-Faugeras constraints.The input of the algorithm is a set of fundamental matrices,and it is unnecessary to perform any projective factorization or projective bundle adjustment.We have developed a step-by-step linear algorithm which avoids unstability of nonlinear problem.Experiments with synthetic and real data have shown that the technique is simple and useful.