A focus detection device having imaging pixels and focus-detecting pixels using a phase-difference focus detection method implements high-precision focus detection. A cylindrical hydrogenous material covered by a boron loaded rubber wrap moderates the center detector within the center tube. The controller may configure the switches in the network to identify broadcast network packets and to forward the broadcast network packets to the controller. The lining may be a preformed elastomer sleeve or formed in situ by the use of a reactive drilling fluid.