An image sensor comprising a row of light sensors registering incident light as electric signals, and a shift register including first and second register places per each light sensor is used for recording frames in fast succession. The image sensor allows for transferring the electric signals from the light sensors to the respective first register places and for shifting the electric signals on selected ones of the first and second register places forward in the shift register. After a first exposure time, the electric signals from each of a plurality of pairs of neighboring light sensors are added on one register place. After a second exposure time, the electric signals from each of the same pairs of neighboring light sensors are added on one register place located between two of the register places on which added electric signals from the first exposure time are present.