Abstract

The critical parameters in the selection of an autofocus cost functional are that it must have a high sensitivity and selectivity at and near the correct focus point and that it must be capable of converging to the correct focus from a large initial or preclosed loop defocus state. The largest initial focal range error an autofocus system is capable of correcting in closed loop is referred to as the depth of convergence. It is shown theoretically and also verified experimentally that the depth of convergence is a sensitive function of the object range, the initial focal range of the imaging system, and, more remarkably, the spatial spectrum of the object.

© 1977 Optical Society of America

Sharpness index and its application to focus control

Ahmed Erteza
Appl. Opt. 15(4) 877-881 (1976)

Effect of detector noise on the positioning accuracy of an autofocus system

Paul J. Caber and Donald K. Cohen
Appl. Opt. 31(31) 6684-6689 (1992)

Spatial frequency sampling by phase modulation as a method of generating multiple images

A. Kalestynski and B. Smolinska
Appl. Opt. 16(8) 2261-2263 (1977)

Laser start-up system for magnetic mirror fusion

A. M. Frank, S. R. Thomas, B. S. Denhoy, and A. K. Chargin
Appl. Opt. 16(5) 1243-1252 (1977)

Synthetic-aperture radar autofocus by maximizing sharpness

J. R. Fienup
Opt. Lett. 25(4) 221-223 (2000)