An objective has a front group, a focus group displaceable along the optical axis and a follow-on lens group having a diaphragm. The front group is arranged at the objective end. The lens group having the diaphragm includes at least two composite lenses and/or two positive lenses and/or the back focus can be adjusted. An objective series is presented wherein all objectives of the series have a uniform appearance and/or the diaphragm is arranged in all objectives proceeding from the image plane at the same location.