1. A method for real-time wavefront sensing of an optical system comprising the following steps: (a) acquiring a first centroid image and determining the positions of the centroids in said first centroid image using a first centroid determining algorithm; (b) acquiring a next centroid image and determining the positions of the centroids in the next centroid image using a second centroid determining algorithm, wherein said second centroid determining algorithm determines the position of each centroid with reference to the position of the respective centroid in the first centroid image.