Diapl is the program based on DIA by Dr. P. Wazniak to do image subtraction. I use diapl2 to reduce my CCD data. When my CCD images' fwhm is about 5 pixels, the results are good, but when the fwhm is 15 pixels (my scale is about 0."28/pixel), the subtracted images are bad. I know that I must adjust the parameters in diapl2, but I do not know whose parameters should be adjused , especially the 'getpsf.par' which has so many parameters. I hope to get help from experienced users. Thanks in advance.