The ZE-X is a most beautiful SLR from the early 1980s. Designed as the top camera for the Mamiya Z series, it offered not only an bayonet mount with electronic connectivity, but also A-, S-, M-, and P-mode. Unlike with other SLR, you wouldn't find a mode dial wheel, however. Instread of the "double control" found in most (all?) other multi-mode SLRs (i. e. mode dial PLUS A-positions on the shutter dial and aperture ring), its design was much more straightforward:
1) put aperture ring and Shutter dial to a specific value (e. g. f5.6 and 1/1000s), and you are in manual mode
2) put shutter dial in "Automatic", and the shutter speed is set automatically - you are in aperture priority mode
3) put aperture ring in "Automatic" position, and the aperture is set automatically, and you are in shutter priority mode
4) put both shutter dial as well as aperture ring in "Automatic" position, and both controls are set automatically (= program mode)
In addition, the camera by default was set to a "crossover mode", which means if your settings can't cope with the existing light, the camera would overrun your chosen (insufficient / wrong) settings and fix the problem. To get a really fully manual mode, this crossover mode could be overrun by the operator by switching a small "MODE" button on top of the camera 
The ZE-X is a pretty rare SLR, and the Mamiya Sekor EF 1.4/50mm is even rarer. Very few images are available of the ZE-X plus EF 1.4/50mm lens, and I haven't seen one with ZE-X & 1.4/50 & Mamiya winder yet!
Unlike any other camera of its time, the ZE-X computer got information about the focus distance set on the lens, at least if a Sekor "EF" lens was coupled. This was used to set the appropriate aperture when using an electronic flash. The aperture set for flash photography was changing continuously from f16 at 1.1 m to f2.8 at 9 m. For even larger distances, the aperture would be opened to f1.4.
The ZE-X has a few more nice features such as
* an exposure override (+(/- 3 EV instead of the more common +/- 2EV)
* Exposure override also working for dedicated flash
* a AE-lock button (quite uncommon back then, but very useful)
* a dedicated switch for multiple exposures
" an electronic self-timer with positions for 2s, 6s and 10s
* a lever for closing the eyepiece / viewfinder
* A slow shutter speed warning (variable with focal length!)
* and even a dedicated electric contacts for a left hand shutter release (!)
To make it short - the Mamiya ZE-X was a very sophisticated SLR for its time. Sadly, its build quality was far from being excellent. Many ZE-X bodies these days have some problems, either concerning the electronics or the rather flimsy mechanical parts. Some obvious problems were adressed already during the rpoduction run (e. g. film rewind - the fork going into the film cartrige was changed from plastics to metal), but other flaws remain. Thus, these days the ZE-X usually will be more of an interesting "museum item" than a SLR used for real world photography ...
It's a bit sad that the Mamiya Z system never came to full fruition. Hints of its potential can be found in the ZE-X manual which shows "f1.2" indicators in the viewfinder. The camera was specifically prepared for lenses longer than 300mm, indicating lenses such as an 1.2/50mm or a tele longer than the existing Sekor E 4/300mm. In 1984, even a "Mamiya ZF" prototyp with AF was announced in the press ...
The Mamiya ZE-X (right) along with its precedessor, the NC-1000. Both cameras are shown with their normal zooms - the NC-1000s with the Sekor CS 3.5/45-90mm and the ZE-X with the Sekor E 3.5-4.3/35-105mm. Both zooms are pretty rare, expecially the CS 3.5/45-90mm.
Mamiya NC-1000s (left) and Mamiya ZE-X (right) with their respective 4/300mm lenses. Again, both lenses are difficult to find, especially the newer Sekor E 4/300mm. The small grip on the ZE-X is quite useful when it comes to larger lenses - not only for the 4/300mm, but also for the 3.8/80-200mm tele zoom.