I think the instructions I've read for the Bronica and an extension tube (I don't have a converter) states that you can mount the tube to the lens first or the camera first. It doesn't matter. What DOES matter is you take the parts off in the same sequence you mount them. That is: mount the tube to the lens, the combo to the camera, take the combo off the camera, then take the tube off the lens. Or vise versa, mount the tube to the camera, then the lens, take of the lens and then the tube. I've found it's easier to remember to mount the tube to the lens first.