1. A method of determining a position of an object with respect to incident radiation, comprising: iteratively determining at least one of an object function indicating one or more characteristics of an object and a probe function indicative of one or more characteristics of incident radiation; iteratively determining the position of the object, wherein the iteratively determining the position of the object comprises; cross correlating first and second estimates of the object, function or the probe function; determining a location of a peak of the cross correlation; determining a translation deviation indicative of a difference in position of the object between the first and second estimates based on the location of the peak.