I'm having trouble maintaining perfect vertical lines with my Canon 30D in the portrait orientation. The NN3 is perfectly level on the tripod, but the vertical lines in my images are just slightly off. Is there an adjustment on the NN3 to fix this? My first thought was that the weight of the camera and lens was too much for the vertical arm of the NN3, but the camera/lens only weighs about 3 pounds. The lines are only slightly off. Any suggestions?