It turns out that a little wear had occurred and some play had been introduced in the rigidity of the front element. Carefully folding and unfolding it I noticed that this part of the mechanism which completes the locking down of the 'front standard' needed assistance.
If you grab your camera (assuming your a Bessa RF owner) you can see here the place I mean. The suraces which the red arrows point to meet when unfolding, and the
arm with the white masking tape on it merges in behind that "can opener" shaped one to lock the front standard (when thinking of the bessa as a non adjustable view camera). This had developed some wear in the mechanism and was allowing the front element to swing a little. This would be desireable in a view camera but its not what you want in a rangefinder ;-)
How I've solved it is to place essentially a small shim over the small arm there. In the photo above I've used masking tape to test the idea, but I've now settled on another simple method that is non-destructive and reversable. I have bent a small section from a aluminum beer can over the arm and secured it with a thin bead of blu-tac. I put the bead of blu-tac it on the inside of the aluminum along where it will sit on the arm. I used the edge of a metal ruler to form the section of aluminum shim so that it folds in a neat "3 sides of a box" and sits neatly over the arm.
This rig now alters the Bessa to have a nice solid front and has returned a snappy feeling to the unfolding (rather than the wobbly feeling before). I've checked the alignment of the lens carefully with both film and ground glass and its been working fine ever since.
Here is a sample of the full width of the horizontal middle of a 6x9 frame at f8
I think that you can easily test your front element by
- unfolding the camera as if taking a photograph
- opening the film door of the camera exposing two light sealing plates at the back (these will allow the camera to sit on the film plane with the lens facing up
- place a flat and light spirit level across the front of the lens
using this you can get an idea how far tilted the lens is from the focal plane (measure in X and Y axis to make sure).
My Bessa is now pretty spot on (as can be seen above)