Variable focus optical system

Abstract

A focusable imaging system particularly suitable for use in acquiring digital images for subsequent processing such as in a hand held, omnidirectional symbology or bar code reader by which linear and two dimensional (matrix, maxi-code) bar codes may be imaged over relatively long working distances. The imaging system includes an focusing objective taking lens and a two-dimensional photodetector that operate to form an image of an object such as a bar code in X and Y directions simultaneously and generate an electrical signal representative of the object or code for subsequent downstream processing by which information embedded in the object or bar code may be extracted. Focusing is achieved via a rotating disk that carries a plurality of optical shims or other light controlling surfaces to provide for different focus zones. A through-the-lens (TTL) targeting system is provided to visually assist the user in positioning the reader for a variety of code modalities to assure that a bar code or the like will be captured within the field of view and be sharply imaged on the photodetector when the lens is focused. Two different forms of artificial illumination are provided to accommodate nearby objects or codes that may be either specular or partially diffuse and more distant objects or codes where the reflection characteristics have less impact on image contrast. Elements of the photodetector are used to assess available light levels and activate the artificial illumination system when ambient light levels are low. Ranging through the lens using elements of the photodetector is included to provide information to set the focus of the objective lens in one of many possible focusing zones.