Jason, it looks like you simply need to adjust the spacing of your mount on your digital back. The Imacon Ixpress usually comes from the factory with a couple of spacers that gives you a 150 or 250 micron (I forget which one it was) spacing between the back itself and the mount. The idea is that you unscrew the mount (ensure you unscrew diagonally opposite screws to prevent flexing of the mount), and change the number of shims in place depending on whether you have back- or front-focus. You can tell which one you have by following the instructions in the shim kit - i.e., place a ruler at 45 degrees to the horizontal, focus an 80mm lens @ f/5.6 at the middle of the ruler with the camera horizontal. In the shot, you will then see if your focus is back- or front-focused from the image, and by how much.
Next step, the shim kit contains shims of different thickness, indicated by how many notches it has - 1 notch for each increment of 50 microns thickness, meaning 1 notch for 50 microns, 2 notches of 100 microns and 3 notches for 150 microns. You will need a bit of trial and error to get the right amount of shims in your back, which might sound like a bit of a pain, but it is worth it because once it is done, you won't need to fiddle with it again. While removing your mount to adjust the shims be careful not to damage your IR filter.
Reason for this shim kit is that each camera, especially in the film era might not have had manufacturing tolerances that were appropriate for digital. So this is the reason why some users might have to shim their back. Not only that, but if you bought your back 2nd hand, the previous user might have shimmed the back already from the factory default, which is what happened in my case - the previous user had removed all the shims altogether and produced a focus error on my camera. I have attached a photo of the Imacon shim kit, what you get, a shot of the instruction sheet and so on.
Jason
p.s. Normally, if I'm not mistaken, a complete Imacon digital back would have come with some extra shims in case you needed to do this. if you don't have any shims, you'll have to visit a Hasselblad dealer to get the shim kit for your Imacon.
