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.
Jim – I have at least one lens that does have three levels of coarseness to the manual focus function of the lens. That’d be the venerable Canon 200mm 1.8L. Now, it is focus by wire and I rarely am not using auto-focus with that lens, but the finest manual focus setting is way to fine for me.
I would think that almost any of the focus rigs for cinema where a gearset is attached to the focusing collar you could easily vary the size of the drive gear, much like changing gears on a bicycle, to affect whatever focusing ratio desired.