The ability to focus electromagnetic fields into a lossy dielectric region is considered for the case where a thin highly conducting sheet is located between the source aperture and the observer. An exact formulation is presented for the aperture illumination which may be any function of the horizontal (x, y) coordinates. The resulting expressions for the fields in the homogeneous dielectric region, above or below the thin conductive sheet, are evaluated numerically for selected cases. In particular, it is shown that the presence of the sheet does not impair the quality of the focus to any major extent, but the amplitude of the field is diminished significantly. The double numerical integration routines are validated by developing relatively simple asymptotic expressions for the fields which also can be employed as dependable field predictors for regions not near the array.