I can't speak to the HCAM Doubleshifter because I have no experience with it. I do, however, have some experience with the Mirex adapter on which it was based, which is why I chose to buy a Cambo Actus instead.
Although the HCAM's movements are indeed "geared" after a fashion, IMO, they are somewhat crude in use compared to the Actus. That's because the movements must be applied in increments of 1 mm by squeezing a tab and sliding a geared rack so it engages the next gear tooth against a pawl, whereas the Actus' rise/fall movements can be applied continuously, in increments of a fraction of a millimeter, by rotating a knob. (Unfortunately, the Actus' shift movement on my model is
not geared at all and is adjusted by sliding alone ...
boo-hiss!)
For the way I work, I greatly prefer the approach Cambo chose. And while I don't use them very often, I do occasionally use the swing and tilt movements when there's no alternative to achieve the DoF I need and the HCAM models don't offer them, so that was another point in favor of the Actus. Of course, the HCAM is noticeably smaller and lighter than the Actus, which in turn allows the use of a less heavy tripod, too, creating even more weight savings. This may not seem like a big deal, but when one of your projects has you carrying the camera / tripod combo around over your shoulder while you're on foot, walking anywhere from three to six miles per outing, even a few ounces of weight savings is noticeable and very much appreciated!
Of course, this is just me and my opinion / personal preference, so YMMV!
For a long time, I wondered about this as well and ultimately had a go at creating one myself, modifying a Cambo Wide DS to accept my A7R body on the back and 35mm format lenses (and medium-format lenses via adapters) on the front:
As you can see, I flipped it on its side, because this had the effect of moving the rise / fall movement to the back of the camera (which, for me, is preferrable to having it on the front of the camera, because this way, the lens doesn't move, minimizing parallax errors when stitching and also eliminating the need to recompose a photo when applying rise / fall movements.) I also added a larger, external battery to power both the 7" HDMI monitor I use and the A7R body, as well as fabricated a bracket to carry a spare lens or two around with me when I'm working away from my car. (Note: I was barely able to make the A7R work and there's no way that an A7RII or III body will work with this setup without, at a minimum, requiring significantly more work -- including machine work -- due to their larger size.)
It actually works very, very well -- except for the movement control knobs being on the front, so one has to operate them blindly, which I find a bit annoying -- and if not for my occasional need to use tilt and swing movements as well, I would favor it over the Actus, because keeping the front and rear standards of the Actus perfectly aligned all the time is by no means guaranteed due to the (IMO) excessive play in its tilt and swing mechanisms. (I've tightened them considerably over how they were set by the factory, but they still drift slightly over the course of an outing. It's probably not a big deal for most people, but when you're trying to stop down the lens aperture as little as possible while achieving the necessary DoF, as I am, because I photograph at night and thanks to Sony's firmware switching the camera files from 13-bit depth to 12-bit depth for exposures longer than 30 seconds, I rarely have any DoF to spare and can't stop-down the aperture any further without making the exposures longer than 30 seconds. As a result, the effects of even very small, but unintended, tilt and swing movements can become visible.)
Although the modifications I performed to the WDS weren't impossibly difficult -- I did everything myself at home, using basic tools and no machine work -- making it possible for the camera to accept 35mm-format lenses did increase the degree of difficulty somewhat, because there was a limit as to how thick the camera could be and still focus the lens at infinity. If one uses only medium-format lenses, however, this restriction will be eased considerably, making a project similar to this one much, much easier to accomplish.
FYI, I did, very briefly, consider modifying an Arca-Swiss Rm3di instead of the Cambo WDS, but the fact that used WDS bodies sell for a fraction of what an Rm3di does was the deciding factor. But as I learned from tinkering with cars, it's always best to start with the version you wish to end up with when you're finished, so if you
really want an Rm3di, then that's what I suggest
you use as
your donor body.
