From Photon to Pixel

2The Photographic Objective Lens

The objective lens has always been considered to be the most important camera component. Certainly, the advent of digital cameras and the emergence of photographic features within systems dedicated to other roles (telephones and tablet computers) have drawn attention to other components, in particular to the sensor (that we will encounter again in Chapter 3) as well as to the numerous accessories of its automatism (that we will detail in Chapter 9). However, we will see in this chapter, that the key role of the lens cannot be denied. It is a complex component whose technical description requires complementary angles of analysis: we will first discuss image formation, in the geometric optics approach, the most relevant in photography, and according to the thin lens model which allows a large number of simple developments (sections 2.1–2.3), then briefly in the case of heterogeneous objectives (fisheyes that do not verify the Gauss conditions (paraxial approximation)) and in the case of thick centered systems, closer to real objective lenses (section 2.4). In section 2.6, we will then examine the role of diffraction to establish the limitations of the geometric approach. We will present the relations that can be established between the position of a point in the image and the position of the object which has given rise to this image in the observed world, and for this purpose we will discuss the basic calibration techniques (section 2.7). Finally, ...