Dynamic focusing lens for expanding depth of focus of optical microscope

Abstract

A dynamic focusing lens for expanding the depth of focus of an optical microscope has been developed. This microscope can be utilized for real-time observation of three-dimensional microstructures. The dynamic focusing lens shifts the focal plane of an objective. When the focal plane is rapidly and continuously shifted along the optical axis, focused and defocused images of each focal plane come into view continuously on an eyepiece or a monitoring screen. However, due to the afterimage of human visual perception, a focused image of the entire object is obtained as if the depth of focus is expanded. The dynamic focusing lens consists of a thin glass diaphragm, of which the diameter is 10 mm and the average thickness is 11 /spl mu/m, a glass plate surrounded by a ring-shaped metal diaphragm, and transparent working fluid sealed between them. Six piezoelectric unimorph piled actuators are located on the upper side to press the metal diaphragm. Pressure of the working fluid deforms the glass diaphragm into convex shape, and the working fluid and the glass diaphragm work as a convex lens. The focal length of the lens can be changed responsively up to 150 Hz. When the dynamic focusing lens is working at 60 Hz, the depth of focus is expanded about four times and the resolution is maintained approximately constant in the range from 0 to 8 mm.