1. An imaging system comprising: a read out unit: for reading out a first image in a first resolution from an imaging device from a first region; for reading out, at a different timing from the reading out of the first image, a second image in a second resolution from the imaging device from a second region within the first region; and for reading out a third image in a third resolution from a third region within the second region, in response to a detection of a characteristic object in the second image, wherein the first to third resolutions are set such that the first resolution is smaller than the second resolution, and that the second resolution is smaller than the third resolution, wherein the imaging system further comprises a distance calculating unit for calculating a distance from the imaging device to an imaging point of the second image, and wherein the second resolution is set based on the distance calculated by the distance calculating unit.