Measuring the refractive power with deflectometry in transmission

We apply "Phase-measuring Deflectometry" (PMD) to the high-precision measurement of refractive power maps in transmission. As is the case for the measurement in reflection a sinusoidal fringe pattern is observed - however in the transmitted light. The local prismatic action of the object under test causes a phase offset in the observed picture, which can be determined by means of well-known phase-shifting techniques. Based on the measured values, the surface power can be determined with an accuracy better than one milli-diopter. We show experiments and discuss the algorithms and the error tolerance. The system supplies traceable data without the need for a special calibration object. The robust and non-expensive method has several possible applications, e.g. the measurement of car glass windows and of eyeglass lenses.