Thanks @Casa. Any images ( preferably with and without focal reducer) which you would like to share?
I am very intrigued by the concept that pictures with the turbo adapter might look better than with a simple adapter. I didn’t consider this initially but after you’ve mentioned that, I’ve given this some thought.
It might be explained with the fact that sensors (unlike film for which these lenses were made) deal rather badly with deflected light coming at an angle on their surface and deal much better with light rays as perpendicular as possible.
By reducing the focal length, the various focal reducers, also reduce the size and the angle of the image circle hence “ straightening" the deflection causing the resulting image to be sharper despite adding glass (which is always going to be detracting from a lens because of added among other things, dispersion).
Of course the better the glass (e.g. low dispersion and other things) you add the better this would be.
Which, ideally would call for a comparative test between the various adapters with high resolution images. One that I haven’t found, yet, on line.
However this might be more true with regard to the center of the image than it is at its corners, which, by the very nature of this idea that sensors deal badly with light coming at an angle, are always at certain disadvantage anyway.
I wonder if it wouldn’t be possible ( WARNING: I have no idea if this is at all possible!) for Fuji to capitalize on this adapter market ( which, let’s admit it, might in fact take something away from their potential sales although adaptive photography is not for everyone) by producing, if this is at all possible, something inspired to the Pentax teleconverter (yes I realize that a teleconverter in not the same as a focal reducer) which came out in the early stages of autofos photography and which made ordinary lens to be somewhat autofocus.
In other words you could take a Fuji made focal reducer with electrical contacts with the camera, put it in between your camera and a “ legacy” lens and have it shift inside to focus the image.
I don’t often engage in fantasy world creations but I’ll indulge myself this time .