In this paper assessment of image quality is restricted to normal photography. That means that we should assess the capability of the lens to give a reproduction of the structures, the colours, and the intensity levels of any object in our surroundings, like landscapes, buildings, technical equipment, or people, animals, and so on. It means furthermore, that we do not look at an aerial image as in a telescope, but that always a photochemical process is included, leading to a projected, slide or to a printed image. The final image is inspected subjectively by the human eye. If we test a lens by measurement of data of an aerial image, the evaluation of the data should take the film, and the eye into account at least in a simplified. way. A second restriction is restriction to black. and white photography. Of course it is possible and desirable to incorporate the assessment of chromatic aberrations. But in this paper we will regard intensities only to keep problems simple.