I bought the NN3 and I have a nikon d50 and a tokina 12-24mm lens. They told me it was able to work, but the only way I can do it is to back the camera on the upper rail until it is off the rail and I have to hold it. This obviously doesn't work because I have to hold it on there and it doesn't stay straight. Do I need the bigger nn5 or is there a way to make this work? Thanks for any advice.