Lessons Learned:
  1. If your C330 photos are out of focus, here are the things to check in approximate order.
    • Push against the filter thread of each lens and ensure the lens plate under it is flush against the camera. If it moves, identify where the gap is. In my case the lens plate was slightly bent and I needed to shim between the silver retaining clip and the plate.
    • Replace the foam under the viewing screen. Keep in mind though that even if the foam is deteriorated it wonít necessarily be the cause of the problem. It needing replacing in my case but wasnít the cause of the out of focus.
    • Ensure you didnít lose a lens shim. Mine are keyed so I couldnít accidentally swap them between the viewing/taking lenses.
    • Adjust the height of the viewing screen by screwing up or down the three posts under it (on the camera body). To ensure the top of these posts lie in a plane perpendicular to the lens plane, use a set of Vernier callipers or a dial gauge to perform measurements. You should be able to get better than +/-0.05mm accuracy here.
  2. If the two lens offsets/heights from the camera body are different, that is OK. (Presuming your other lenses are also adjusted accordingly, but in my case I have no other lenses).
  3. Use proper test equipment suitable for the task at hand. For example I purchased a dial gauge to measure the parallelism of the lens plane on the camera body/bellows. I made the mistake of not having a sufficiently flat surface under the film rails. I used what I thought was a square/flat block of wood, on a laminated benchtop, but the combination wasnít level to <0.05mm. This mistake lead me down a very long and wrong path (see below). I solved this problem by having a thick block of Perspex cut to size to fit snug on the film rails and than sat that and the dial gauge on another flat sheet of larger Perspex. (see prior images in this thread for setup photos)
  4. The reason I thought the lens planeís supposed non-parallelism was worth pursuing was because the service manual instructs one to test for parallelism and had a mechanism for adjusting it if it was out. I then wasted lots of time pulling the side of the camera off only to be unable to unscrew a final plate (thankfully). After that didnít work, I then tried shimming the lens plate away from the camera and removing one lens shim. All then looked good with the comparisons using a loupe at the lens plane, but that method only adjusted the centre of the viewing field for equal focus !! The way I found out it was wrong is when I had run a few rolls of film through and kept getting a non vertical/sloping depth of field in my shots !! (even after meticulously levelling the camera and target sheet of paper).
I hope this experience helps at least one other person in the future if their C330 or TLR is not focusing correctly. In fact, Iím willing to bet there would be quite a few cameras of all flavours (both analog and digital) out there with their focus out of calibration, but their users are oblivious to it !