We describe a solar-blind UV imaging photon detector with an extended dynamic range which can be used to record very faint UV sources. This detector includes an RbCsTe photocathode, microchannel plates (MCPs) and a two-dimensional resistive anode. It is coupled with an objective lens and a UV filter which rejects daylight with an optical density higher than 12 for experiments performed outdoors at sea level. In order to increase the relatively small dynamic range of the detector due to local saturation in the MCP, a method based on control of the proximity voltage between the photocathode and the MCP has been developed. Control is performed remotely by a TTL signal. It regulates the detected event rate within a pre-defined interval. The system spatial and temporal performance has been studied in detail. A comparison between the results obtained with and without gating has been made and confirms the interest of our new acquisition system for measuring radiometric quantities of low light level sources over an extended dynamic range.