Before we start, we need to make a guess as to that magic rotation point mentioned previously. This is where the misinformation comes in. 1. The point the camera must rotate about is the entrance pupil, not the nodal point as is often stated. Better yet, who cares what they call it, there's a test to figure it out.2. The rotation point (entrance pupil) is NOT necessarily halfway down the lens. In fact, on many cameras, it's not even close to that. So, what's the test to find the entrance pupil?Our mount will hold the camera sideways, but for now it's easiest just to hold it horizontally. Position two objects on a table so that they line up when viewed through your lens - a couple of batteries work perfectly for this. Now pan your lens right and left as you normally would. You'll see the objects move relative to each other - that's parallax. Now, let's find a better pivot point. Put the tip of the index finger of your left hand somewhere along the bottom of the barrel of the lens. Now rotate the camera about that point. Try to hold that left hand as steady as possible (c'mon, you're a photographer, you got steady hands, right?) Still see a shift? Move your finger/pivot point along the lens until that shift goes away. On my Canon 17-85 EF-S, the point was 4 1/8 inches forward of the screw socket.This photo shows the camera straight ahead, and the batteries aligned:
Now the camera is turned to the side. The alignment is quite close, but not perfect - we can see the left edge of the rear battery poking out:
[Edited by Moderator on 12/19/2009 4:50:46 AM]