Height variation of a tilted specimen may alter the magnification and image rotation because of re-focusing with an objective lens. Evaluating the height of the tilted specimen by means of the objective excitation, we derive approximate expressions for the alteration of the magnification and the image rotation. They are in the form of a second-order expansion of the lens-current variation. Theoretical results are validated by measurements in an ultra-high-voltage electron microscope. These expressions are especially useful for correcting images in the quantitative application to electron tomography.