There, it is great to know that my tutorial will be helpful for someone. It only takes a few measurements really, and might be a boring process of screwing in and out the screen between tests. Basically if you have the original shims, they are measured to the right distance. If you lose them, use your hand or anything to lift up the focusing screen very slightly until focus is just about right, and estimate/measure that distance. Now use shims which are the same thickness.