Like the much older 60mm Micro Nikkor this lens has ONLY a front lens filter thread. This means that the R1C1 Macro Flash can only be attached to the front lens element and not to the barrel of the lens. The weight of several macro flash heads (up to eight possible) is considerable.For the 60 mm Micro Nikkor Nikon therefore provides the more than flimsy UR-5 adapter ring, so that the R1C1 can be attached to the barrel and not the front element of the lens. The new 40 mm DX Macro does not permit this. The R1C1 can ONLY be attached to the front lens, not the barrel. This incurs considerable wear on that extruding and moving front element and essentially means that this new MACRO lens is incompatible with Nikon's own Macro flash. Incredible!