A technique for automatically focusing the lens of an electronic still camera employs a progressive scan image sensor 20 with a fast dump structure 62. The image sensor 20 itself is operated first in a "fast flush " mode to focus a lens 22, and then in a normal readout mode to obtain the final still image. To focus the lens 22, an image is integrated on the sensor 20. The average contrast of a central region 66 of the image is used to determine how well the image is focused. The portion of the image surrounding a central focusing area 66 is rapidly read out and discarded, using "fast flush" clocking where the vertical and horizontal registers are continuously clocked and lines of image charge are dumped to the substrate through the fast dump structure 62. In the central focusing area 66, a pattern of lines are eliminated through the fast dump structure 62, and the intervening lines are transferred out to generate a focus adjustment signal. The process is repeated numerous times as the lens focus is adjusted until the maximum average contrast is obtained. At this point, the entire sensor is cleared using "fast flush" clocking, and the final image is then captured and read out.