Hi Vladimir, Obviously, I can't do Ronchi testing right either. The test program I am using, Ronwin20, shows three lines either side of center when I set it for the parameters of the mirror. 16.5" diamter. 149.5 ROC. 100 lines per inch grating. 0 offset. What is wrong? Clear skies, Jerry _______________________________________________ ATM mailing list http://www.atmlist.net/