Do you have the ATM books yet? Willmann-Bell recently reorganized them and added more info to the original set and I would recommend that you get the full set. I think that book 3 (new set)(or is it book 2) has a section on making EP's. The books are very usefull for a large number of things and should be on your bookshelf of well used books if you are into building things astronomical. The designs are old by today's standards (done in the Porter days) but are quite workable for the slower scopes where you don't have to correct for wide acceptance angles. Have Fun and Keep Looking Up! Bob May