The imaging properties of a model high aperture fluorescence confocal microscope are studied by way of numerical methods. The model consists of an aberration-free high aperture objective illuminated by a monochromatic linear or circular polarized light source, and a detection system equipped with a finite sized pinhole. The computation of the intensity distribution near the confocal plane is based on electromagnetic diffraction theory. We study the 3-D imaging properties of the model by examining the images of three different objects; points, lines and planes. We calculate the resolving power for these objects as a function of their orientation and the size of the detector pinhole. The results indicate the necessity for image analysis schemes to take these effects into account.