The IQ series backs are capable of producing such high quality images that every aspect of their capture needs careful consideration. For instance, large format lenses specially designed for digital capture can produce incredible resolution and clarity. Especially wide angles.
If your subject has special requirements such as architecture or shooting product photography, then your IQ series back will attach directly to a technical camera. This is where Phase One's approach to medium format photography really excels.
You can take the IQ series back off your 645DF and attach it to any other camera such as this Alpa.
So how does the digital back communicate with a manual camera? The IQ series backs have two modes. There is zero latency and normal latency. In normal latency the digital camera sends a message to the back to wake it up just before exposure. In zero latency the back is always on. So when you fire the shutter from a technical camera the back is ready to roll.
To synchronize the digital back with the lens shutter when using a technical camera, you need to connect a sync cable between the lenses' flash sync and the digital back's multi connector port. I set the shutter latency on the IQ series back to zero which means that the back is always ready for capture when the shutter is fired. This means you can use a standard sync cable between the lens and the IQ back. However, zero latency does use more battery power.
The alternative is to leave the back set to normal latency and then use a special two shot cable. What this means is just before you take the photograph, you press the little button on the cable that wakes up the back, and then you make your exposure.
With technical cameras, a lens cast calibration, or LCC, is made to ensure consistent color and exposure over the entire frame. Of course the big change for technical camera uses is the live view feature found on the new IQ series backs. No longer do you have to worry about external view finders, or focusing on the ground glass. You can view the image as the center is going to see it directly on your LCD screen. You can get very precise framing and of course your focusing is absolutely correct.
It really doesn't matter what type of camera you want to use. The Phase One IQ series backs have everything covered.