What Is Meant by Performance Evaluation

The performance characteristics of an imaging optical system can be represented in many ways. Often the final optical performance specification is in terms of the modulation transfer function (MTF), encircled energy, rms blur diameter, or other image quality criteria. These criteria relate in different ways to the image quality of the system. Image quality can be thought of as resolution or how close two objects can approach each other while still being resolved or distinguished from one another. Image quality can also be thought of as image sharpness, crispness, or contrast.

As discussed earlier, imagery is never perfect. It is limited by geometrical aberrations, diffraction, the effects of manufacturing and assembly errors, and other factors. The characterization of image quality by the methods described in the following sections will help you to assess just how your system performs with respect to its imagery.

It is important to realize that the image quality or resolution of the entire system is not totally dependent on the optics, but may include the sensor, electronics, display device, and/or other system components making up the system. For example, if the eye is the sensor, it can accommodate for both defocus and field curvature, whereas a flat sensor such as a CCD cannot. In this chapter, we will be discussing only the optics contribution to image quality.

What Is Resolution?

When we think about the image quality of an image-forming optical system such as a camera lens, the first...