Complex sentence: Most modern SLR cameras use through-the-lens optical AF sensors, with a separate sensor array providing light metering, although the latter can be programmed to prioritise its metering to the same area as one or more of the AF sensors.
Split into simpler sentences: Most modern SLR cameras use through-the-lens optical AF sensors, with a separate sensor array providing light metering. Although this can be programmed to prioritise its metering to the same area as one or more of the AF sensors.