Focus adjustment-free imaging over a long range

Focus adjustment-free imaging over a long range is demonstrated, both theor etically and experimentally, by using a simple telescopic system of the Gal ilean type that has an eyepiece with specified spherical aberration. Comput er simulation results show that such a telescopic system with a 5 cm apertu re can form clear images of a target over a range from 60 to similar to 400 m, without focusing adjustment. The imaging results of an experiment carri ed out using such a telescopic system confirm that clear images can indeed be obtained in this range without focusing adjustment, verifying the useful ness of the new technique. (C) 1999 Elsevier Science B.V. All rights reserv ed.