Approach with 2 wedges. The aim was to find a simple mechanism that allows for high precision. If you tighten the screw the lower wedge moves left and pushes up the upper wedge with the camera on top of it. If you loosen the screw the camera moves down. Because of its simplicity it would be less susceptible to errors.
You can download the model here: Media:ModelWedges.zip. You need to have Google SketchUp installed to open the model.