Played with it for a while today. Quite an incredible piece of kit and for me, elevates the Arca platform to a whole new level of usability and realization of the quality of latest crop of MFDBs and tech lenses.
You essentially pick your point of focus using the optical finder. This registers the distance. The lens is extremely fast, so focus is quite easy.
This gives a corresponding DoF for 5.6/8/1/16 for your selected lens profile. The helical can then be dialled in to match what you want, and this is displayed right below the eModule reading. Couple of impressive things here, a) the lens profile is not based on some formulae, but rather on the behaviour of the particular lens. So focus shift issues are accounted for automatically. I was focussing a 35XL at 3-4ft with incredible accuracy; b) You now have the flexibility to place you subject at any point within the DoF - again you see the both scales at the same time on the LCD, I think this is really cool, particularly when shooting at distances with wide lenses. I have never seen the IQ focus mask light up so consistently before, either with LV focus or using the helical with charts. You really appreciate the refinement of the helical focus system, the charts are far too course.
Lens profiles are factory loaded. Similar to the base infinity calibration for the helical, you calibrate this along with the OVF. Same thing for the built in levelling system. All DoF scales and focus information is based on a base CoC that is entered as well. Options allow for 5/6/7/8/9/10/20/30/40 microns.
Nice. A little bigger than I expected, but typical arca quality, a combination of metal and high-grade plastic. The lens in the OVF is by SK and as soon as you look through it, you realize it has some science behind it.
Typical Arca - form follows function, no surprise there. Lots of button combinations, for setup, but once done, quite simple to use. The module can also be removed and used off camera while tethered with an RJ9 straight through cable. This would be convenient for planning your shot. Battery is a built in, weather tested rig.
Things I don't know yet and would be nice:
Multiple profiles for lenses - this would allow far more flexibility IR and other spectrum uses. Also, a user programable interface would be cool. Combining the OVF with the Arca Vario-finder would be icing on the cake! I'm sure our good friends at Arca have big plans.
This one did not have the profile for the 32HR, but the mine, that should be shipping next week will. Now that I have seen and played with it in the flesh, I am quite confident this thing is for real.
I am glad they took their time with this one. I have not experienced a more accurate focussing system -- Canon 1's, Nikons, LV etc.