It is shown that, in general, the size of the image of a point source generated by time-reversed wave-front devices is governed by considerations similar to those determining the resolving power of lenses. If the device subtends an angle α at the image, then the image has a lateral dimension ~λ/sin α. However, in some cases, when α is large and the imaging device is thin or the laser beams have special polarizations, images several times larger might be obtained.