I'm trying to decide what mount I need.
I want to take multi-row panos using a Canon EOS400D and will probably be using a Sigma 105mm fixed focal lens. I had hoped to use the NN3.

My problem is that the data for the NN3 gives a measurement of 107mm for the length of the camera from back of camera to tip of lens. The sigma is way beyond this, in fact even the kit 18-55mm lens is beyond this by 20mm or so.

For a multi row pano do I really need to worry about this measurement, I don't need to point the camera directly up or down, so what is the limiting factor, why is this 107mm measurement so small?