1. A method of determining a position of an object with respect to incident radiation, comprising: determining, at a detector, an intensity of radiation scattered by an object; iteratively determining, by a processing device, at least one of an object function indicating one or more characteristics of the object and a probe function indicative of one or more characteristics of radiation incident on the object; iteratively determining, by the processing device, the position of the object, wherein the iteratively determining the position of the object comprises: cross correlating, by the processing device, first and second estimates of the object function or the probe function; determining, by the processing device, a location of a peak of the cross correlation; determining, by the processing device, a translation deviation indicative of an improvement in determination of the position of the object with respect to the radiation incident on the object between the first and second estimates based on the location of the peak; wherein the iteratively determining, by the processing device, at least one of the object function and the probe function comprises determining, by the processing device, a third estimate of the object function or the probe function based on the translation deviation; and outputting one or more of the object function, probe function and an indication of the position of the object.