Ikelite Modular 1.75 Inch Extension Ring with FocusIkelite Modular 1. 75 Inch Extension Ring with Focus 551075 Ikelite Product Number 5510. 75 Product Details A special extension is available for use with Nikon 105mm VR Macro and Canon 100mm USM Macro lenses. Manual focus is adjusted with a large, easy to turn knob on the side of the extension. Extension can be used with the Nikon 105mm VR Macro lens and either 5510. 16 or 5510. 22 Lens Extensions. Canon 100mm USM lenses require the 5510. 16 Lens