Pieter... it's a "selective focus" type thing...
focus is achieved by manually squeezing the front element towards the camera (it's preset at infinity... well actually this particular one focused beyond infinity) to focus closer.
due to its design you only get a small area around the center of the front element that is in focus, the sides of the front element can never be in focus as the simple design of the lens doesn't allow light rays passing through the outer edges to converge on the focal plane.
So what you do is you shift the front element sideways/up/down to change what part of the front element strikes what part of the film/sensor plane and there by shifting what part of the frame is with in the central focus area. you can also tilt the front element to create a narrower field of focus and some (though not much as you'd think) tilt effect.
You can change the aperture by dropping in Waterhouse Stop disks but it doesn't do anything sharpness wise (especially edge sharpness) apart from change the DoF in the central focus area and change the EV (requiring corresponding inverse EV change in shutter speed to maintain exposure ratio)
An acquired taste and a specialist tool that, in the end, I couldn't see myself using much beyond its initial novelty period
