Originally Posted by
dave_whatever
It's definitely a rack and pinion like any other similar camera (Ebony, Walker, ShenHao etc). The toothed track is on the underside of each standard carrier, and geared axle is inlaid into the base of the camera, and hence both not visible in the above photo.
The only difference between the focussing on Chamonix H models and other comparable field cameras is that the focus runs very loosely and lightly compared to Ebony etc. The locking mechanism functionally is the same as on an Ebony or ShenHao, but there is less inbuilt friction in the running forwards and backwards of the standards. This gives rise to the issue described by the OP where you have to hang onto the focus knob when locking otherwise locking will push the focus forwards/backwards (also if you point the camera downwards without the focus locked the weight of the lens can pull the front bed out). It can be mitigated to an extent by partially tightening the locking knob before focussing.