VARIABLE FOCUS OPTICAL SYSTEM

A variable focus optical system is particularly suitable for use in acquiring digital images for subsequent processing in a hand held, omnidirectional symbology or bar code reader (12) by which linear and two dimensional (matrix, maxi-code) bar codes (28; 34; 40; 52; 54) may be imaged over relatively long working distances. The imaging system includes a focusing objective taking lens (92) and a two-dimensional photodetector (93) that operate to form an image of an object such as a bar code in X and Y directions simultaneously and generates an electrical signal representative of the object or code for subsequent downstream processing. Focusing is achieved via a rotating disk (94) that carries a plurality of optical shims (130) 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 system for a variety of objects to assure that an object will be captured within the field of view and be sharply imaged on the photodetector (93) when the lens (92) is focused. Two different forms of artificial illumination are provided to accommodate nearby objects that may be either specular or partially diffuse and more distant objects where the reflection characteristics have less impact on image contrast. Ranging through the lens (92) using elements of the photodetector (93) is included to provide information to set the focus of the objective lens (92) in one of many possible focusing zones.