Designed for exclusive use with a Macro-Nikkor 105mm F/4 fitted with a meter coupling ridge (AI, AIS-type), the PN-11 ring enables you to cover a reproduction ratio range of 1:1/2 to 1:1. Full-aperture metering and automatic maximum aperture indexing apply when the ring is used with cameras fitted with a meter coupling lever (AI-type cameras). The ring is fitted with a rotating tripod collar at the balance point of the camera/ring/lens combination. The collar is threaded to accept standard 1/4 inch tripod screws, and permits photography with the camera positioned either vertically or horizontally. Important! This ring cannot be used with a non-AI type Micro-Nikkor 105mm F/4 lenses.