Step 5: The 3 threaded rod legs
The 3 threaded rods I used were 8mm diameter but this is not critical. The length of the rods will depend on the distance the camera has to be from the document to just frame it perfectly. The best way to determine the distance is to measure it. Use a test document with the largest length, width and smallest text you are going to work with, set the camera for the widest view and the right focus range. Move as close as possible to just frame the whole document, keep as steady as possible and take a few test shots. Remember the page should be in portrait mode so turn the camera to suit - don't waste any pixels! Check your shots have a good focus and readability. Once you have the settings worked out get someone to measure the distance from the camera mounting screw hole to the test page when you are at the right distance to suit your camera.
This distance plus about 2-3 inches to allow for the other components, is the minimum length for the threaded rods. You could add a bit more to allow for photographing documents a bit bigger than A4 like I did; I ended up with rods 18 ½” long.
The rods are held onto the base board with two nuts and two washers.