An optical system for imaging an object on an image acquisition unit. The optical system, from the object, comprises a first lens unit, a second lens unit, a third lens unit and a fourth lens unit in the direction of the image acquisition unit. The first lens unit comprises at least one lens group with negative refractive power. The second lens unit comprises at least one lens group with positive refractive power and the third lens unit comprises at least one lens group with negative refractive power. The second lens unit and the third lens unit overall comprise at least three lens groups. From the first lens unit in the direction of an image acquisition unit, the first lens group, the second lens group and then the third lens group are arranged. The three lens groups have a movable design for adjusting the focal length of the optical system.