1. A system for iris image acquisition, the system comprising: a sensor configured to acquire a plurality of images including a first image of an iris of the subject; a memory; and at least one processor configured to: generating a quality metric of the acquired first image for comparison with that of one or more images stored in a memory, the quality metric generated by determining a proportion of the area of the iris that is exposed within the acquired first image and available for biometric matching, and a sharpness or contrast of features in the acquired first image; responsive to the generated quality metric, storing the acquired first image of the iris in the memory by overwriting an image stored in the memory or including the first image while staying within a predetermined maximum number of images allowed to be stored in the memory, if the quality metric is higher than that of at least one of the one or more images stored in the memory; and a focus controller component, configured to control a controllable focusing component to focus at a predetermined series of different values within a focus range for acquiring the plurality of images, without any input from measurement of whether an image of the subject to be acquired is in focus or out of focus, and to scan over a range of focus values until the subject departs from a corresponding acquisition region or a predefined number of images having a quality metric exceeding a predetermined threshold is acquired.