This book presents the basic knowledge necessary to understand how optics is involved in instruments. The role of optical instruments is very important and affects all areas of human activity, offering an essential part of the instrument, but which are not always visible. It is therefore useful and important to show how optics works. This book presents a review of existing components used, the theoretical elements and an example of evolution. The basic theories, principles and components available are described. This book is an introduction to other books in the series devoted to biology and medicine, and instruments used in the space industry as well as more complex books. The first chapter discusses the place of the optical equipment in modern instrumentation. The role of the light source, external or internal to the system, strongly depends on the purpose of the instrument. Chapter two recalls the foundations of geometrical optics. Chapter three is devoted to aspects of photometry and taking into account the energy flux carried. It gives photometric and radiometric definitions, and the photometric properties of the instruments. The main sources used are summarized in Chapter four with a short review of the main used sources: lamps, lasers, laser diode, LED,OLED.The role of the light source, external or internal to the system, strongly depends on the purpose of the instrument. The characterization of a color, its representation and its return is the subject of Chapter five. The fundamental laws of colorimetry, color perception, evaluation of color are described. Chapter six deals with mathematical methods to restore the image quality obtained and derive the maximum information: mathematical study of image analysis, image classification, image interpretation- morphology mathematic, LIP(Logarithmic Image Processing) model. Chapter seven and Chapter eight provide examples of modern industrial systems. The first gives a short review of objectives for photography, cinema, television and astronomy, the second describes devices with intensifier of light, band SWIR, bands 3-5µm and 8-12 µm. The last chapter gives an example of the evolution from conventional microscopy to modern microscopy: Modulation Transfert Function (MTF)- STED (Stimulated Emission Depletion Microscope), Phase microscope, Tunneling microscope, Near field microscope.