In this paper, we compare two complementary approaches to determine the imaging quality of the photometer. The first approach is based on a direct camera measurement of the point-spread function (PSF) while the second approach uses a Shack-Hartmann sensor to reconstruct the wave front of the system.
Both methods yield in principle largely overlapping information in terms of e.g. modulation transfer function (MTF), encircled energy (EE) or spot shape. However, the experimental requirements are quite different. Details like the spatial extent and coherence properties of the object have different impact and are essential for the degree of agreement between both approaches. Moreover, the disturbance due to measurement noise is quite unequal and requires different evaluation steps.
The pros and cons of both methods that actually complement one another are investigated and discussed.