The AP-554 replaces the stock foot on the Nikon 200-400mm f/4 or 500mm f/4. It is an alternative to our AP-553 plate. It has the advantage of greater clearance between the body of the lens and the foot, making it easier to use the foot as a handle for your lens. In addition, it is longer, allowing you to balance your lens properly when using light-weight camera bodies. It will allow you to balance your lens with all pro and pro-sumer Nikon camera bodies, even when using teleconverters (see chart below for details). It is the only replacement foot on the market for these lenses that allows this comprehensiveness in balancing. We used finite element analysis to design the foot with the proper balance of weight savings and stiffness. Other manufacturers have removed material to make the product lighter; however, we found that doing so reduces its rigidity below our quality standards.