Experimental characterization of an autofocus algorithm based on liquid lens objective for in-focus imaging in the macro range

The experimental characterization of an autofocus algorithm using a liquid lens objective is presented. The objective embeds an electro-wetting based lens whose focal length is voltage controlled. Two sharpness indexes are used to measure the image focus condition in the algorithm allowing a very robust and accurate setting of the focus. The algorithm has been characterized using target images differing both in the contrast and in the spatial frequency along measurement depth range from 70 to 2 mm. both static and dynamic tests were performed revealing the ability of the algorithm to follow rapid variations of the target position.