The AV110 was developed for the use of auto focus lenses in the U-A series of Ewa-marine housings. The function of the AV110 is to ensure a fixed and rigid connection of the housing's front port to the tripod thread under the camera's body. This then allows the autofocus to lengthen or shorten the effective length of the lens without beeing effected by the surrounding water. Without the AV110 the lenses motor would have to "pump" air from the rear of the housing to the front, and vice versa, during focussing. This definitely exceeds the design specification of the motor and could lead to damages of the lenses mechanics.