Study on influencing factors of measuring precision of OTF measurement instrument

Optical Transfer Function(OTF) Measurement is well known as the more accurate and more comprehensive method that is used in evaluating the imaging quality of optical systems. Nowadays almost all optical companies and national standard institutes use the OTF measurement instruments as the most reliable image evaluation systems. But in the actually measuring process, it is frequent that the measuring results of the same sample are variable by using different instruments. The reason is that the subsystems of the OTF measurement instrument have inherent errors, which made the different OTF measurement instruments have dissimilar measuring precisions. In addition, temperature and the resulting thermal expansion dynamics of the mechanical set-up become factors limiting the performance of OTF measurement instruments. In this paper, the fundamental theories of OTF measurement instrument were introduced, including its mathematical model, measuring principle, basic structure and so on. Then the influences of inherent errors of subsystems and the thermal expansion dynamics of the mechanical set-up on OTF measurement instrument were also discussed in detail. Based on the analyses of this paper, it is obvious that the OTF value measured by OTF measurement instrument can only be treated as a sort of relative benchmark. However, this relative benchmark can also produces feedback on the performances of optical systems by rule and line in time. And it always has the main effect in guiding the design, machining, assembly, debugging and any other process of production.