The answer is that you can focus stack with the Fuji 120/4 on a rail just fine, as illustrated by this test I did yesterday at 1:2:
http://blog.kasson.com/the-last-word/fuji-1204-macro-at-12-on-gfx-loca-and-focus-shift/
Jim
Focus stacking on a rail is, according to Rik Littlefield (designer of Zerene Stacker) the least friendly to stacking software way to capture stacks. A real question I have had when moving to fly-by-wire systems such as the Hasselblad X1D or the Fuji GFX, both systems which I purchased, is what’s with fly-by-wire focus as relates to stacking-focus? All of the lenses, for example, that are native to the Hasselblad X1D use fly-by-wire technology for focus. The standard reasons for moving to fly-by-wire are that it is less expensive, makes it easier to implement auto-focus, and (supposedly) less and less photographers are bothering with manual focus.
Whatever the reasons, I wanted to know what effect (if any) does fly-by-wire technology have on stacking focus? It worried me because not only have I never used fly-by-wire focusing, but I don’t even use auto-focus... much. So what gives?
Fly-by-focus drives some folks crazy because on lenses that use it, they are no distance scales, etc. listed. And the reason for that is because with fly-by-wire there is no direct mechanical linkage between turning the barrel and a certain distance. While fly-by-wire systems may differ, it is possible to turn off the camera with a particular point in focus, turn it back on, and the focus point may have jumped to some other area of the subject. Again: there is no mechanical linkage as we have in traditional lenses.
Also, long focus throws don’t seem to exist in the fly-by-wire focus systems I have tried, although, of course, you can get a particular point in focus. For those of us into close-up macro focus-stacking, having a decent-to-long focus throw is a distinct advantage. For example, one of the best corrected lenses, the Coastal Optics 60mm APO f/4 lens has a focus throw of around 210-degrees, while the Leica 100mm Elmarit-R f/2.8 APO lens has a focus throw of more like 720-degrees. The net result is that the Coastal Optics lenses really has to be placed on a focus rail to get the kind of gradual focusing that is often required. Not a good design IMO.
With the proper EVF or LiveView screen and magnification, it is possible to focus accurately using one of these fly-by-wire-focus lenses. We all know it is easy to focus a one-shot photo, and I have determined that shooting a “short stack” imaged by focus-stacking also works well enough. But what about the more-standard focus-stacking method of 15-100 layers? How does the fly-by-wire stack up (pun intended) to the more traditional mechanical helicoid method of stacking focus.
To check this, I photographed two stacks of around 20 layers, one using the fly-by-wire and single-stepping it (like we usually do) and a second stack of the same fly-by-wire lens mounted on a focus rail and moved mechanically. I used the Hasselblad X1D with the 90mm f/3.5 lens.
The results showed that both methods produced a usable stack.
