The accuracy of calibration patterns, their fabrication, and their setup are some of the important challenges in a zoom-lens camera calibration process. We address these problems by using a cross-diffractive optical element, which generates a virtual, dense, and robust calibration grid. We show that a 33×33 calibration grid provides enough control points to fill the entire field of view for 10 to 20× zoom lenses. We show that the calibration of a zoom camera at infinity can be done using this method. A polynomial function has been used to model the variation of the intrinsic calibration parameters over the zoom range. The obtained calibration model has also been validated using a well-known target pattern.