[en] The minimum distance of resolved bubbles in a perfect optical system--with experimental results in not too bad disagreement-does not take into account practical limitations from two sources: the quality of the optical system, and the resulting depth of field. Optical aberrations due to the bubble chamber and vacuum tank windows are studied. The use of an obstructing anular pupil to increase depth of field is considered. The superiority of the holographic method to any classical method, because of its unlimited depth of field, is also discussed