chapter  2
34 Pages

Visual Optics

WithJim Schwiegerling

The design of optical systems requires an understanding of the conditions and environment under which the system will be used. In addition to the performance of the optics, the characteristics of the scene and its illumination, as well as the capabilities of the „nal image sensor, need to be taken into consideration. Failure to incorporate the scene and sensor into the design process can lead to mismatches between components and unnecessary underor overspeci„cation of component performance. As a simple example of this mismatch, consider a diffraction-limited F/2 lens coupled with a 1/3-inch Video Graphics Array (VGA) Charged-Coupled Device (CCD) array as the image sensor. A diffraction-limited system has an Airy pattern as its point spread function. The size of this spot is proportional to the „rst zero crossing of the Airy disk. For a wavelength of 0.5896 μm, the diffraction-limited spot diameter produced by the lens is given by

Spot diameter = 2.44λ(F/#) = 2.8 μm (2.1)

The image sensor, however, has overall rectangular dimensions of 4.8 × 3.6 mm and 640 × 480 pixels. Each pixel is therefore 7.5 μm square. Consequently, there is a performance mismatch between the optics and the sensor, where the optics can resolve features approximately three times smaller

CONTENTS

2.1 Introduction .................................................................................................. 37 2.2 The Human Eye and Visual System ..........................................................38 2.3 Photopic Response and Colorimetry ........................................................43 2.4 Chromatic Aberration .................................................................................55 2.5 Resolution and Contrast ............................................................................. 57 2.6 Head-Mounted Display Example .............................................................. 61 2.7 Summary .......................................................................................................68 References ............................................................................................................... 69

than what the sensor can resolve. Such a mismatch suggests that either the performance of the optics can be reduced or the pixel density of the sensor can be increased, depending on the speci„c imaging application.