Abstract: A closed-loop circuit arrangement sequentially operates in a tracking mode before the shutter of a single lens reflex camera is actuated, and then in a holding mode after the shutter is actuated. The circuit arrangement receives from a conventional photoelectric circuit a first analog signal that instantaneously represents exposure time so long as light entering the camera impinges on the photoelectric circuit. A register in the circuit arrangement provides a digital multi-bit signal that is converted to a second analog signal. The first and second analog signals are compared to produce an error signal used during the tracking mode in controlling the register so that the digital multi-bit signal varies until the first and second analog signals represent the same exposure time. After the shutter is actuated, the register serves as a memory thereby causing the second analog signal to statically represent exposure time.