I’ve been using the Cambo Actus and the HR Digaron 180/5.6 for a while. One of the things that has bothered me is how difficult it has been to focus critically. The standard focusing adjustment mechanism is just too coarse. Combo has a fix for that. Like most Cambo products, it comes at considerable cost, but in the spirit of “in for a penny, in for a pound”, I ordered the Cambo AC-380 fine ratio geared focus assembly.
It’s two concentric knobs driving the Cambo rail gearing. The inner, larger knob has the same ratio as the standard Cambo focusing knob, while the outer, smaller knob requires five times the motion to move the back standard the same distance.
It works great. You can focus coarsely with the inner knob just as you did with the standard focus assembly — actually better than that, since the knob is larger . Then you can use the outer knob to easily trim the focus.
Makes me wonder why we don’t see lenses with fine and coarse focusing rings.