Autocollimators comply with the requirements of different metrological measurement tasks. These instruments are compact, versatile and easy to use. Angle deviations of prisms, polygons, e.g., are measured with autocollimators. If calibrated electronic autocollimators are used, then the measurements can be performed with uncertainties down to 0.01 arc sec. However, the uncertainty might be increased by one order of magnitude or more if surfaces with small apertures, aberrant surfaces or surfaces placed at long working distances are measured. To define the measuring window, respectively the limiting parameters, a software based model of the optical system was implemented. Aberrations, diffraction, temporal and spatial coherence were taken into account. To increase the measurement range, now defined by simulations of the optical system, a phase grating technology can be used. Simulations assuming a phase grating technology show a significant enhancement of the autocollimators imaging properties. This enables a significant reduction of the uncertainty at difficult measurement tasks as mentioned above. The state of the art of simulations will be presented and the optical
background will be described.