An active disturbance rejection controller was designed in the lensbarrel of an aerial camera to reduce the disturbance caused by an eccentric cam of the lensbarrel. An extended state observer was designed to estimate the disturbance and then to generate control signals to compensate the disturbance influence. First, the disturbance characteristic of the cam was analyzed. And then, a mathematic model of lensbarrel was established and simplified. Based on bandwidth parameterization,the extended state observer and the control law with disturbance compensation were designed and a position controller was finished. Finally, an experiment on the lensbarrel was performed to test the disturbance rejection performance of the controller. As compared with the traditional first order square lag-lead compensation method used in aerial cameras, experiment results show that the active disturbance rejection controller can reduce the disturbance error about 50% with a lower controller gain about percentile. In conclusion,the disturbance rejection performance of the system is improved and the demand for controller gain is lowered at the same time. It is feasible and practical.