This lens ring allows photographers to use the Vü 150mm Professional Filter Holder System with the unthreaded Tamron 15-30mm f/2.8 DI VC USD lens. Due to the construction of this particular lens, a specialized lens ring is required specifically for this lens. It also requires the separate purchase of the Vü 150mm Professional Filter Holder (VFH150) to be fully funtional with the Vü 150mm Professional Filter Holder System.