US Patent 7872819 Lens barrel and imaging apparatus

When an external force that is equal to or greater than the urging force of a first ball spring is applied to a first lens holder, a first ball follower is dislocated from a first cam groove, and a first external force receiving groove and a first external force receiving pin are brought into engagement to receive the external force. When the external force that has been applied to the first lens holder is released, the first ball follower is restored to the first cam groove due to the urging force of the first ball spring.