The object and its sky is observed as described before, but for deconvolution, a separate star for evaluating the point spread function (PSF) has to be observed. It should be of about the same brightness and color as the object and as close as possible. Because the telescope has to be moved each time when switching from the object to the PSF reference, there will be a big loss in effective integration time (few minutes per telescope movement). But one should not hesitate to spend this time for well calibrated data. The observation of the PSF reference is carried out in the same way as the object.