A new calibration method is proposed for calibrating cameras with large lens distortion, using a planar grid pattern. The distortions are adjusted with an iterative algorithm. When the points on each curve in the image of the grid pattern are fitted with a linear equation in the image space, the distortion correction factors are determined. The camera's optical center is obtained through a Hough transform. Then, a group of linear equations and a cubic equation are established in the corrected image space. The remaining parameters of the camera are then deduced. Only one view of a planar grid pattern is needed for this method. The experimental results verify the effectiveness of the proposed method.