A cannula assembly including a seal for an endoscopic internal magnetic camera tether. The seal may include stacked compliant membranes with an aperture in each membrane through which a camera tether may pass. The apertures may overlap. The at least one aperture may be arranged as a slit. Each of the apertures may comprise a wedge-shaped gap. The membranes may include engagement members that couple to engagement members on the cannula assembly. The cannula assembly may provide separate ports for the camera tethers and for a trocar or other endoscopic instrument passing through the cannula assembly. The cannula assembly also may include a rotating housing with two openings and a seal arranged in each opening. The cannula assembly may include a sleeve that encases a cannula tube. The sleeve may include a seal on its end and a channel on its periphery through which a camera tether may pass.