Over the past fifteen years we have evaluated numerous models of accommodation. Our task is to clarify these models by designing an automatically focused camera, with major emphasis of the capability of the retina to sense blur and feed this information back to the eye's lens for accurate focal adjustment.Oepth-of-field, or dead-band, poses a significant obstacle for the designer of an automatically focused camera. Our approach I s to use noise to provide a scanning, or dither motion so that the lens will spend 80 percent of its time in sharp focus. Retina detection of blur can be simulated by a Charge Coupled Device (CCD), designed to produce a null when sharpest focus is achieved. The nature of blank-field accommodation is judged, and a prediction made about its long-term behavior.

We present an efficient approach to compute the second-order scattering of an electromagnetic wave by two discrete scatterers in proximity to each other. Such a two-body system represents the simplest canonical arrangement to address near-field volume scattering phenomena in microwave remote sensing models of vegetation. Using an analytical wave-based approach, a successive scattering methodology is employed to derive the first interaction term in multiple scattering by two arbitrary scatterers in terms of their transition operators. The general formulation is applied to find the second-order bistatic scattering amplitude for a pair of finite length thin cylinders at arbitrary interaction distances using the exact Green's function. To improve computational efficiency, the solution is then specialized to the Fresnel region. These second-order bistatic scattering amplitude results are in agreement with the exact Green's function model when the scatterers are in the Fresnel region of each other. Additionally, it is demonstrated that using the far field approximation in the Fresnel region can yield significant deviations from the exact results. The Fresnel model, unlike the far field approximation, accurately predicts the scattering amplitude peak values and null locations, and is suited to fast solutions in realistic canopy simulations.