Focus adjustment-free imaging over a long range

Abstract Focus adjustment-free imaging over a long range is demonstrated, both theoretically and experimentally, by using a simple telescopic system of the Galilean type that has an eyepiece with specified spherical aberration. Computer simulation results show that such a telescopic system with a 5 cm aperture can form clear images of a target over a range from 60 to ∼400 m, without focusing adjustment. The imaging results of an experiment carried out using such a telescopic system confirm that clear images can indeed be obtained in this range without focusing adjustment, verifying the usefulness of the new technique.