I recently acquired a set of extension tubes for my Universal Press. The trouble is, I have no idea how they work. How does one focus using these babies? The Mamiya manual is less than helpful. Cheers,
There is a ground glass back for the Universal and Super 23 which accepts sheet film holders. That would be one method. Another would be to use the ground glass back to focus and carefully replace with roll film holder. That's the only way I know.