what failures did you run into. Send me what you have. If the focus was off from the center of the mirror being off I may have a solution. In making a dob, you replace the secndary mirror with a shperical convex 2" to 3" mirror. Then you have the makings for a Schmidt. But instead of drilling a hole in the center of the primary, you install a diagonal. Now the light will shoot out to the side. Guess where you put the focuser? Directly at the pivot point. Look, a dob spins up and down on two wheels. If the focuser was in the center of one of those wheels then you would do two things. You wouldn't have to stand up sit down fight fight fight. All the eyepieces would be at one level. And by making the scope into a pseudo schmidt you eliminate 30% of the light source or so coming from the center of the dob. I forget what they call it when you use the ronchi test and gring the center to parabolize the mirror but most of the problems come from the center being off. I think. Email me with anything you might have to help me make a 20 and a 30 inch scope.