Remote eye tracking systems are widely used evaluation tools in many disciplines. Such systems have to deal with free head motions that cause a defocussing of the camera image. Hence, remote eye tracking systems usually have a limited operating range. This contribution presents a novel auto-focus setup for a small and mobile remote gaze tracking system that enables a clear eye image acquisition in a large operating range. Therefore, our setup uses a miniature liquid lens to achieve smallest possible focusing latencies and installation space. Using this technology, we extended the eye tracking system's operating range to distances from 0.6 m up to 1.3 m, with a mean accuracy of 0.45° in 4 exemplary working distances.