Practical Measurement Issues

In this chapter, we will consider a variety of practical issues related to MTF measurement, including the cascade property of MTF multiplication, the quality of the auxiliary optics such as collimators and relay lenses, the issue of source coherence, and the finite size of the source for a PSF or LSF test. We will also look at the instrumental-MTF contribution of the detector or the sensor array that receives the image-irradiance data. We will investigate ways to increase the signal-to-noise ratio, making use of redundancy in the source and image planes. We will conclude with some comments about repeatability and accuracy of MTF measurements and the use of computers for data acquisition and processing. At the end of the chapter we will consider four different instrument approaches that are representative of commercial MTF equipment, and identify the design tradeoffs that were made.