1. A method for determining a set of optical imaging functions which describe the imaging of a measuring volume ( 10 ) onto each of a plurality of detector surfaces on which the measuring volume ( 10 ) can be imaged at in each case a different observation angle by means of detector optics, comprising the steps: a) performing pre-calibration, during which for each detector surface the assignment of each volume position (X, Y, Z) in the measuring volume ( 10 ) to an image position (x i , y i ) is determined on the respective detector surface, b) simultaneous imaging of the measuring volume ( 10 ), in which a plurality of optically detectable particles ( 12 ) are distributed, on the detector surfaces, c) determining of support positions, namely of the volume positions (X, Y, Z) of at least a few particles ( 12 ), from corresponding image positions (x i ,y i ) of particle images in the images ( 20 , 22 , 24 ) of the measuring volume ( 10 ) generated in step b by application of a triangulation method based upon the assignments determined in step a, d) improving the assignments determined in step a by using the support positions determined in step c, so that a set of improved assignments results as a set of the imaging functions to be determined, characterized in that a shape model, parameterized by shape parameters (a, b, φ, I) and having the shape with which a particle ( 12 ) in the measuring volume ( 10 ) is imaged onto the detector surfaces, is predetermined, and in that step d of improving the determined assignments comprises the steps: d1) determining of values of the shape parameters (a, b, φ, I) for the support positions determined in step c, using the corresponding particle images, d2) estimating of values of the shape parameters (a, b, φ, I) for all volume positions (X, Y, Z) of the measuring volume ( 10 ) by application of a mathematical adaptation method based upon the values of the shape parameters (a, b, φ, I) determined in step d1 for the support positions, d3) issuance of a set of imaging functions which, for each detector surface, assign to each volume position (X, Y, Z) of the measuring volume ( 10 ) a corresponding image position (x i , y i ) as well as the corresponding shape parameter values (a i , b i , φ i I i ) estimated in step d2 or determined in step d1.