A capacitor for use in RF probes, especially for use with a thin-film oxide superconductor NMR probe coil is provided. Further objects of the invention are to reduce the effect of the HTS coil on the uniformity of the polarizing field throughout the sample volume, to provide a capacitor for use with an NMR coil with increased RF current-carrying capability of the coils and/or with reduced electric fields from the coil which fringe into the sample volume and hence less noise. These and other objects of the invention are met by providing a capacitor comprising a thin film of conductive material on a planar substrate, the film comprising a first elongate tapered finger and a second elongate tapered finger, each finger (50) having a wide end and a narrow end; the wide end of the first finger being proximately disposed to the narrow end of the second finger and the narrow end of the first finger being proximately disposed to the wide end of the second finger, adjacent fingers forming a uniform gap (52) therebetween, whereby a capacitive element is formed between the first and the second finger.