1. A method for simulating an aerial image generated by imaging an object with the use of an imaging optic, the object being illuminated by an illuminating optic by using a light source emitting illuminating radiation, the illuminating optic having a pupil plane, the method comprising: defining a first data set to represent the object; defining a second data set to represent the intensity distribution of the illuminating radiation in the pupil plane of said light source; and calculating, using a data processor, the aerial image from the first and the second data set; wherein the resolution of the second data set varies according to the intensity in the pupil plane or according to the location within the pupil plane.