A lithography projection objective for imaging a pattern in an object plane onto a substrate in an image plane. The projection objective comprises a multiplicity of optical elements along an optical axis. The optical elements comprise a first group of optical elements following the object plane, and a last optical element, following the first group and next to the image plane. The projection objective is tunable or tuned with respect to aberrations for the case that the volume between the last optical element and the image plane is filled by an immersion medium with a refractive index substantially greater than 1. The position of the last optical element is adjustable in the direction of the optical axis. A positioning device is provided that positions at least the last optical element during immersion operation such that aberrations induced by disturbance are at least partially compensated.