This Letter presents an optical design method based on the Seidel aberration theory for dynamic refocus systems. The function of a dynamic refocus system is to increase the amount of return photons when a pulsed laser travels over an extended height range. In this study, the dynamic refocus system is a short focal image system. The aberrations of the dynamic refocus system are calculated individually. Aplanatic lenses are used to eliminate the main spherical aberration. A field lens is used to change the stop position in order to eliminate comas and astigmatism. The effectiveness of the initial design results are confirmed, and the designed dynamic refocus objective with an aperture of F-number 0.98 and a focal length of 14.325 mm is achieved. The total motion of the dynamic refocus mirror is approximately 216 μm at heights that ranged from 8 to 18 km. The optimum result shows that the dynamic refocus system is an ideal optical image system at each conjugating height with 10 km sample thicknesses.