A method of aligning at least two wave shaping elements, a method of measuring a deviation of an optical surface from a target shape and a measuring apparatus for interferometrically measuring a deviation of an optical surface from a target shape. The method of aligning at least two wave shaping elements, each of which wave shaping elements has a diffractive measurement structure for adapting part of a wave front of incoming light to a respective portion of the target shape, includes: providing a first one of the wave shaping elements with a diffractive alignment structure, arranging the wave shaping elements relative to each other such that each of the diffractive measurement structures is traversed by a separate subset of rays of the incoming light during operation of the measuring apparatus, and aligning the first wave shaping element and a second one of the wave shaping elements relative to each other by evaluating alignment light having consecutively interacted with the diffractive alignment structure and with the second wave shaping element.