I do believe that Zernike did up a test like that, using spots on a plate to obtain a Foucault like test on all directions. A perusal of Malacara's book on testing will probably find the test. Bob May http://nav.to/bobmay bobmay@nethere.com NEW! http://bobmay.astronomy.net _______________________________________________ ATM mailing list http://www.atmlist.net/