A method includes counting a first set of photons having times of flight that falls within a first time range and being detected during a first time period, determining a second time range based on the first set of photons, the second time range being smaller than the first time range, counting a second set of photons having times of flight that fall within the second time range and being detected during a second time period, and determining a third time range based on the second set of photons, the third time range being smaller than the second time range.