1. A method for determining a critical angle of total reflection, comprising: illuminating a sample with an excitation light beam of a light source; using an image capturing sensor, capturing fluorescence images at a plurality of different angles of incidence of the excitation light beam, wherein each of the fluorescence images comprises a first image area including an object to be examined and a second image area outside the object; and using a processor, determining a critical angle of total reflection at an interface of the sample based upon an analysis of the fluorescence images, wherein said analysis comprises: forming for each fluorescence image an intensity ratio between a first fluorescence intensity in the first image area of one of the fluorescence images and a second fluorescence intensity in the second image area of said one of the fluorescence images, wherein said ratio being formed by dividing one of the first and second fluorescence intensities by the other of the first and second fluorescence intensities; and evaluating the intensity ratios for the plurality of angles of incidence.