These illustrations show how the focus knob works.
The first image shows the top half of the camera as viewed a little to the left of the straight-on view a subject would have.
This is our standard product. In this illustration, the focus knob is set for a subject distance of about 10 inches. The camera can focus as close as 4 inches. Focused at that shortest distance, the focus knob would extend another inch or so higher than this.
The next image is a close up of the first view.
This shows a little more of the details of scale imprinted on the focus cylinder and, at the back, the witness mark for the focus.
When the focus is set at infinity, the focus cylinder is all the way down as shown in the next view. This view is from the back of the camera and represents the operator's view.
The fourth and final view is also from the back. It shows the focus knob removed and has the focus mechanism set for a focal distance of 30 inches.