In an optical distance sensor for measuring object surfaces with high precision and comprising an objective lens for focusing a measuring beam to a measuring spot on the surfaces, measuring errors due to tilt of an object surface can be detected by using a pupil monitor, which senses the radiation intensity distribution of the reflected measuring beam effectively in the pupil of the objective lens to generate a tilt signal, which can be supplied to a correction/calibration table to obtain a correction signal, which is suitable for correcting the primary distance measuring signal of the sensor. Especially for a differential confocal distance sensor having pinholes arranged in front of radiation-sensitive detectors, a further order of correction can be obtained by determining optimum position and diameter of these pinholes.