Method for ascertaining an optical flow using an image sequence recorded by a camera of a vehicle, wherein the method comprises the following steps: receiving at least one input signal, which represents a vehicle environment and/or driving situation of the vehicle recognized using at least one sensor of the vehicle, and/or a result from a previous ascertainment of the optical flow, and an image signal representing the image sequence; determining a time difference value (Δt) using the input signal; selecting at least two frames (502; 602; 702; 900) of the image sequence which are offset from one another by the time difference value (Δt), using the image signal; and detecting matching pixels in the frames (502; 602; 702; 900) in order to ascertain the optical flow using the matching pixels, wherein, in the determination step, at least one further time difference value which deviates from the time difference value (Δt) is determined using the input signal, characterized in that the further time difference value represents a longer time difference than the time difference value (Δt), wherein, in the selection step, at least two further frames of the image sequence which are offset from one another by the further time difference value are selected, wherein, in the detection step, matching further pixels in the further frames are detected in order to ascertain the optical flow using the matching further pixels, wherein, in an evaluation step, the frames (502; 602; 702; 900) are evaluated in order to ascertain the optical flow for an ego-movement and surface estimation in a first region of the vehicle environment, and the further frames are used to ascertain the optical flow for an estimation of the relative speed between the vehicle and vehicles driving in front in a second region of the vehicle environment. receiving at least one input signal, which represents a vehicle environment and/or driving situation of the vehicle recognized using at least one sensor of the vehicle, and/or a result from a previous ascertainment of the optical flow, and an image signal representing the image sequence; determining a time difference value (Δt) using the input signal; selecting at least two frames (502; 602; 702; 900) of the image sequence which are offset from one another by the time difference value (Δt), using the image signal; and detecting matching pixels in the frames (502; 602; 702; 900) in order to ascertain the optical flow using the matching pixels, wherein, in the determination step, at least one further time difference value which deviates from the time difference value (Δt) is determined using the input signal, characterized in that the further time difference value represents a longer time difference than the time difference value (Δt), wherein, in the selection step, at least two further frames of the image sequence which are offset from one another by the further time difference value are selected, wherein, in the detection step, matching further pixels in the further frames are detected in order to ascertain the optical flow using the matching further pixels, wherein, in an evaluation step, the frames (502; 602; 702; 900) are evaluated in order to ascertain the optical flow for an ego-movement and surface estimation in a first region of the vehicle environment, and the further frames are used to ascertain the optical flow for an estimation of the relative speed between the vehicle and vehicles driving in front in a second region of the vehicle environment.