Next, cut the arm. To figure out the length, start with that previously measured distance between the entrance pupil and the screw socket (the one that was 4 1/8 inches on my Canon) - this distance is shown in green above. Add a half inch to an inch on either side. The width need only be a couple inches. Drill a hole at one end for the arm to attach to the side piece where it will pivot. Drill another hole 4 1/8 inches (or whatever your measurement is) down the arm towards its other end. This last hole is where the camera attaches, so it needs to be 1/4" wide. Insert a 1/4-20 thumb screw through this hole (1/4-20 means 1/4" wide, with a thread pitch of 20, which is the most common pitch)./hosted/tutorials/112588_thumb screw.jpgNow, attach the arm to the side. You'll need a flathead machine screw - you may have to gouge out a bit of the hole in the arm so the full head can sink into the arm and not hit your lens:
Push the screw through the arm, then through the side, then use a washer and a wingnut to secure it. [Edited by Moderator on 12/19/2009 4:55:29 AM]