English: A simulation of spherical aberration in an optical system with a circular, unobstructed aperture admitting a monochromatic point source. These are longitudinal sections through the focus, and scaled to f/1. Inside focus is to the left, and outside-focus is to the right (i.e., light is propagating left to right). The top image is over-corrected (half a wavelength), the middle image is perfectly corrected, and the bottom image is under-corrected (half a wavelength). Note the left/right reversal of the top and bottom images. While this simulation was computed under the rubric of en:fourier optics, you can compare these images to commonly drawn diagrams in en:geometric optics. See also the corresponding focal plane images.