Method and apparatus for performing an automatic focus operation for a

Abstract

A method for quickly performing an auto-focus operation on a confocal microscope. As a coarse Z-stage moves a target toward an objective lens, a photodetector generates an analog electronic focus signal which exceeds a threshold level during a focused condition. When a focused condition exists, a latching comparator, which is coupled to the electronic focus signal and to a signal representative of the threshold level, trips and the target is stopped. The analog nature of the electronic focus signal assures that the focused condition will be detected. As a result, the target may be moved quickly without missing a focused condition. The target is moved several times at progressively slower velocities to position the target close to the focus position. In another embodiment of the present invention, an auto focus operation is performed by positioning the target such that a focus position is within the range of motion of the target, moving the target a plurality of first steps through its range of motion, and measuring the strength of a focus signal at each first step. The target is sequentially moved a multiplicity of second steps through a second range of motion on either side of the first step at which the maximum strength was measured. The strength of the focus signal is measured at each of these second steps. The target is moved to the second step at which the maximum strength was measured.