I bought the NN3-MKII for my Nikon D90 and Nikon VR ED 24-120 3.5-5.6 lens. The upper arm does not stay in place (it keeps coming down). The camera lens combination weight less than 3 pounds. In selecting the NN3 pano head I followed the product selector page of the website. Can anybody give me advise on what I am doing wrong? Where I can find the right settings for this camera lens combination?