Optics in Instruments

Chapter 2

Formation of Images ¹

This chapter is about the formation of images by an optical instrument. The “first” example of an optical instrument is the eye. The light diffused by a lighted object that we see is concentrated by the cornea and the lens of the eye onto the retina. Thus we can say that the image of the object is formed on the retina. We can also say that cavemen practiced optics without knowing it. A brief history of this science and its principal protagonists can be found in the introduction to Eugène Hecht’s book Optique [HEC 05].

This chapterisdivided intofourmain parts. Thefirstisanintroductiontogeometrical optics and its approximation, optics in Gaussian conditions. The second part deals with the main properties of an optical system or instrument. In fact, this part is not exhaustive and is continued in the next chapter. The third part considers the problem of geometrical aberrations. Chromatic aberrations form the topic of the fourth part.

2.1. Introduction to optics

Optical instruments can be divided into two categories:

– objective instruments which form the image of an object on a receptor. The best example of such objectivity is in photography, which allows us to obtain the image on a film or a digital sensor. Slide projectors and overhead projectors also belong to this category;

– subjective instruments which work along with the eye to observe objects. These objects may be very near, in which case we use a magnifying glass or a microscope. These objects ...