1. An iris imaging system comprising a camera that captures images of irises within a predefined capture volume with sufficient resolution for biometric identification, the camera including: an optical system including an objective lens, and an adaptive optics loop that auto-focuses an image of an iris onto an image plane located at a fixed position based on a reflection of light from an eye containing the iris, with an image scale and an image spatial resolution that is constant regardless of a standoff distance to the iris, the adaptive optics loop comprising: a deformable mirror that adjusts a wavefront of the eye reflected light; a wavefront sensor that senses the wavefront of the eye reflected light; and a controller coupled between the deformable mirror and the wavefront sensor that adjusts the deformable mirror based on the sensed wavefront; and a sensor array located at the image plane.