1. A subjective refractor for determining refractive error of the eye comprising: an optical system configured to generate a predicted depth of focus of the eye and including an optical lens for presenting at least two targets to the eye, the two targets separated along the optical axis of the lens thereby providing a difference of focus between the at least two targets as observed by the eye and such that the difference of focus between the two targets is greater than the predicted depth of focus of the eye; means for indicating target preference from the presented targets; the target preference including an indication of target clarity; focus altering means for presenting again the at least two targets to the same eye such that the targets are dioptrically offset by a predetermined value in the direction of the preferred target based on the target preference; and means for determining refractive error of the eye on the basis of target preference.